SEARCH

SEARCH BY CITATION

Keywords:

  • breast neoplasms;
  • mammography;
  • screening;
  • race;
  • African Americans;
  • density;
  • obesity;
  • age;
  • ethnicity

Abstract

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

BACKGROUND

Notwithstanding some controversy regarding the benefits of screening mammography, it is generally assumed that the effects are the same for women of all race/ethnic groups. Yet evidence for its efficacy from clinical trial studies comes primarily from the study of white women. It is likely that mammography is equally efficacious in white and African American women when applied under relatively optimal clinical trial conditions, but in actual practice African Americans may not be receiving equal benefit, as reflected in their later stage at diagnosis and greater mortality.

METHODS

Initial searches of Medline using search terms related to screening mammography, race, and other selected topics were supplemented with national data that are routinely published for cancer surveillance. Factors that potentially compromise the benefits of mammography as it is delivered in the current health care system to African American women were examined.

RESULTS

While there have been significant improvements in mammography screening utilization, observational data suggest that African American women may still not be receiving the full benefit. Potential explanatory factors include low use of repeat screening, inadequate followup for abnormal exams, higher prevalence of obesity and, possibly, breast density, and other biologic factors that contribute to younger age at diagnosis.

CONCLUSIONS

Further study of biologic factors that may contribute to limited mammography efficacy and poorer breast cancer outcomes in African American women is needed. In addition, strategies to increase repeat mammography screening and to ensure that women obtain needed followup of abnormal mammograms may increase early detection and improve survival among African Americans. Notwithstanding earlier age at diagnosis for African American women, mammography screening before age 40 years is not recommended, but screening of women aged 40–49 years is particularly critical. Cancer 2003;97(1 Suppl):258–72. © 2003 American Cancer Society.

DOI 10.1002/cncr.11022

An erratum to this article is published in Cancer (2003) 97(8) 2047.

Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death among women in the United States.1 Until there are well established primary prevention strategies that will benefit the general population of women at risk, secondary prevention in the form of mammographic screening represents an important strategy for reducing mortality from this disease. Mammography has been shown to reduce breast cancer mortality in women aged 50–69 years by as much as 30%.2 Although there has been some controversy, recent studies have shown that the benefit of reduced breast cancer mortality may also come from mammographic screening of women aged 40–49 years.3

In the current article, we consider screening mammography in the African American population. Specifically, we raise the question of whether African American women receive the full benefit of this secondary prevention strategy. There is good reason for asking this question, given the long-standing and seemingly persistent race disparity in breast cancer morbidity and mortality observed in population data.4 Clearly, the efficacy of a screening strategy goes beyond the technical aspects of early detection; it also encompasses more practical issues, such as access to testing, notification of results, compliance with recommended followup of abnormal exams, and regular (repeat) screenings in compliance with recommended intervals. It is not difficult to imagine that the overlap between racial identity, cultural identity, and socioeconomic status may translate into observable race/ethnic differences in breast health outcomes. Against this background, our current objective was to identify areas in which more research is needed and/or a more innovative approach is required to ensure that African American women receive the maximum benefit of this important screening strategy. The specific issues discussed include the following:

  • evidence for efficacy of screening mammography in African American women from clinical trials and observational studies;

  • compliance with mammography screening in African-American women;

  • potential impact of ethnic variation in breast density and obesity on screening mammography yield; and

  • adequacy of current screening mammography guidelines for young African American women.

A definitive evaluation of each of these issues is somewhat constrained by the gaps in the scientific literature. Standard search techniques were used to review Medline for publications that were related to screening mammography, race, and other selected topics. National data that are routinely published for cancer surveillance are also referenced. Yet for some questions race-specific data were not available, thus making it necessary to conjecture about the effects in African American women based on studies of this screening modality in white women. Because the large body of research devoted to social, medical, behavioral, and psychologic factors that influence access to screening has been addressed by others5–7 and is somewhat tangential to the question of efficacy of mammography screening in African American women, these issues are not addressed in detail in the current review.

Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

While screening mammography is generally assumed to be an effective screening tool in all race/ethnic groups, the current review of clinical trials and observational studies found limited race-specific data, as described below.

Clinical trial data

The efficacy of screening mammography based on clinical trial data has been extensively reviewed, and, irrespective of recent challenges,8, 9 there is general agreement that screening confers benefit to women aged 50–69 years, whereas the benefits to younger women have only recently been more widely accepted.2, 3, 10 However, limited attention has been given to whether these results apply to African American women. To our knowledge, among the eight randomized clinical trials that have evaluated screening mammography,11–20 only the Health Insurance Plan of Greater New York (HIP) Study11 included a substantial proportion (approximately 20%) of black participants and provided race-specific results.21, 22 In a single report of race-specific survival rates, Shapiro et al. showed that substantially more white than black women in the control group survived breast cancer five years from diagnosis (60.9 % versus 47.1 %). In contrast, very similar five year survival rates were observed (73.4 % and 76.6 %, respectively) among whites and blacks in the group that was offered mammography screening. These results are consistent with the hypothesis that race parity in mammography screening might offset the poorer breast cancer survival observed among African Americans. While this is an encouraging finding, the study had several limitations. These included: 1) very low statistical power to show a race difference in survival in the study group, due to the small sample of nonwhite breast cancer cases and 2) a lower proportion among nonwhite subjects of axiliary nodal involvement in the study group as compared with the control group.22

Observational data

Because of the paucity of clinical trial data, observational studies play a critical role in the assessment of screening mammography efficacy in African Americans. In addition, these data provide insights into the efficacy of mammography as it is delivered in the current health care system rather than under the more ideal clinical trial conditions. We reviewed studies that examined: 1) the success of mammography screening programs that included African American women; 2) the explanatory effect of lower mammography utilization in African Americans on the observed race differences in stage at diagnosis of breast cancer; and 3) trends in breast cancer mortality by race in relation to trends in mammography use.

The influence of a screening program on breast cancer survival was examined using data from the Breast Cancer Detection Demonstration Project (BCDDP), which provided five years of annual screening to over 280,000 women, including 5.1% non-Hispanic blacks.23 While reported results suggest an overall benefit associated with screening,24, 25 to our knowledge, there are no published reports that detail race-specific findings.

Race-specific information on breast cancer stage at diagnosis was collected by the National Breast and Cervical Cancer Early Detection Program (NBCCDP), which provided mammograms to over 570,000 medically underserved women (53.7% white, 16.2% African American, 19% Hispanic, 3.2% Asian/Pacific Islander, 5.8% American Indian/Alaska native, and 2.1% other/ unknown race) across the country between July 1991 and March 1998. The proportions of women whose breast cancers were detected early (cancer in situ or localized) increased from the first to subsequent mammography screening rounds, 55.2% to 71.1% in white women and 49.7% to 62.4% in African Americans. Although medically underserved African American women who participated in the NBCCEDP showed an increase in early stage cancers with subsequent screening, they continued to be diagnosed with later-stage cancer more frequently than medically underserved white women.26 Similarly, in a primarily low-income African American population participating in the Breast Cancer Screening Program (BCSP) of Cook County Hospital in Chicago, diagnoses of localized breast cancer (in contrast to regional and distant disease) significantly increased five years after the program's inception. However, the proportion of BCSP participants diagnosed with early-stage disease remained significantly lower than the proportion of white women diagnosed with early-stage breast cancer throughout Illinois during the same time period.27

Prior mammography use has not been found to play a major role in explaining the observed later stage at diagnosis among African American women compared with white women. As an explanatory variable, Jones et al. found that prior mammography screening accounted for only 9.4% of the race difference in stage at diagnosis in multivariate analyses.28 McCarthy et al. found that mammography history explained a slightly greater proportion of the race difference in stage at diagnosis (12%) when adjusted for sociodemographic factors and comorbidity,29 although even here the influence of mammography is not substantial. Results from the first study of this type, the National Cancer Institute's (NCI) Black/White Cancer Survival Study, also indicated that mammography screening history played a negligible explanatory role, once other variables were introduced into the model.30

Trends in late-stage diagnosis indicate a narrowing of the black–white gap in the proportions of women diagnosed with regional and distant stage breast cancers from 1988 to 1995 (Surveillance, Epidemiology and End Results [SEER] data).31 Trends in breast cancer mortality show a decrease among white women aged 40–79 years from 1989 to 1992. While a similar decline was not observed among African American women,32 it appears that breast cancer mortality in this group may have stabilized in recent years.33 These diagnostic stage and mortality trends occurred during a period of increased mammography use among African Americans, suggesting a benefit, albeit more modest than that in whites.33 Whether this race/ethnic disparity stems from less use of repeat screening mammography or from the relatively lower efficacy of this screening tool in African Americans34 cannot be ascertained from these studies.

Receipt of Screening Mammograms Among African Americans

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

From the literature on participation in mammography screening, several screening behaviors are generally monitored: 1) one-time use of mammography; 2) recent mammography screening; and 3) repeat screening. With regard to these outcomes, we describe trends in mammography use in African Americans over time and across age groups, comparing these findings with trends in mammography use among white women. Further, we discuss compliance with followup of abnormal screening exams. We also examine the relationship between socioeconomic status (SES) and screening behavior in African Americans.

One-time and recent mammography screening

Numerous studies have examined whether a woman has ever had a mammogram or undergone recent screening, and several of these studies have included African Americans. We do not present a comprehensive review of these studies. Instead, we focus on data from The National Health Interview Survey (NHIS) and the Behavioral Risk Factor Surveillance System (BRFSS) that have tracked mammography screening behavior in the national population over time and are used to establish state and national screening goals (e.g., Healthy People 2010). With regard to the validity of these self-reported mammography data, several investigators have found strong agreement (82% to 94%) between women's reports of mammograms obtained in the past year and medical record data.35–37 Mammography reports provided by African American women were less likely to agree with medical records than the reports of white women.37, 38 However, in evaluating these results, the potential for inaccuracies in medical records and in data abstraction must be considered.38

Survey data have shown that the proportions of African American and white women who have ever had a mammogram have increased dramatically over time.39, 40 Data from the BRFSS indicate that the age-adjusted percentages of African American women aged 40 years and over reporting having ever been screened increased from 63.8% in 1989 to 85.1% in 1997. A similar increase (from 64.5% to 84.9%) occurred in white women over the same time period. In addition, projections for 2010, based on Missouri BRFSS data, suggest that the proportions of African American and white women who report ever having had a mammogram will continue to increase.41 However, the relative parity, on a national level, in the proportions of African American and white women who have ever been screened is not found in all areas of the country. In Mississippi and Arkansas, for example, where screening percentages across race/ethnic groups in 1997 were relatively low (64.7% and 56.5%, respectively), the gap between white and African American women in one-time screening was substantial (67.9% vs. 56.1% in Mississippi and 58.7% vs. 44.3% in Arkansas).42

As one might expect, among African Americans and whites, the proportions of women receiving a recent mammogram are somewhat lower than the proportions of those ever screened, but, as with one-time screening, these proportions have been increasing over time. In 1987, the NHIS found that only 24% of African Americans and 29.6% of whites ages 40 and over had been screened in the preceding two years, whereas by 2000 these percentages had increased to 67.8% and 71.4%, respectively.43

Because the incidence of breast cancer diagnosed under the age of 50 years is slightly higher among African American than white women,44 and average age at diagnosis is significantly lower in African American than white breast cancer patients,45 particular attention should be paid to adequate screening of younger African Americans. Assuming that mammography is an effective screening tool in this age group, it is encouraging that national data find that relatively large proportions of 40 to 49 year old African Americans have undergone recent screening, in some cases exceeding proportions in white women in the same age range.40 Still, the proportions of women in their 40s who have been screened are somewhat lower than among women in their 50s and 60s.43 Some increase in screening among women ages 40–49 years is likely in the coming years as the recommendation for annual mammography screening of women in this age group, instituted by the American Cancer Society in 1997, becomes standard practice.46 The proportions of elderly women obtaining recent mammograms are also low, as compared with women in the 50-69 year age range in both races. Because of the increased incidence of breast cancer with age,44 this screening deficiency may also require attention in both race/ethnic groups.

Repeat mammography screening

The above data and other recent studies found little difference in the proportions of African Americans and whites who were ever or recently screened.47–51 This has prompted some to conclude that the race gap in mammography use that was apparent in the 1980s is no longer present.52 However, a careful examination of repeat screening behavior by race is needed before such a conclusion is reached. Assessment of regular or repeat mammography is a potentially more important measure of screening behavior than whether a woman has ever had a mammogram or has had a recent screening because it is unlikely that one mammogram will meaningfully influence the probability of early breast cancer detection and improved survival,53 whereas a lifelong habit of mammography may meaningfully reduce breast cancer mortality risk.

Accordingly, we undertook an extensive review of the literature on repeat mammography screening. Compared to studies of one-time and recent use, we found relatively few studies of repeat screening behavior and still fewer that addressed repeat screening by race. In Table 1, we have summarized studies that provided data on repeat screening in African American women. Most but not all also included data on white women. Because of the limited number of studies, we defined repeat screening broadly and included those studies that assessed whether consecutive screenings had been obtained, as well as those that examined some combination of having obtained past screening(s) with intention to screen at regular intervals in the future. We excluded studies that examined compliance with recommended screening guidelines when, in fact, this variable was defined as having had a mammogram in the past year; a more accurate description of these data would be recent screening. We also excluded one clinical trial (HIP) that did include race-specific data on repeat mammography screening because intensive efforts to optimize participation in mammography screening were undertaken in that investigation.21 Thus, screening compliance reported for that trial cannot be validly compared with compliance in the observational studies reviewed here.

Table 1. Repeat Screening Mammography Among African American and White Women
Author/dateData collection method/datesPopulation/nAge in years% African AmericanaRepeat screening definedRepeat screening resultsDifference in repeat screening between African Americans and whites
African AmericanWhite
  • a

    Remaining percentage is white unless otherwise noted.

  • b

    Percentages calculated based on data presented.

  • BMI: body mass index; HMO: health maintenance organization; MD: medical doctor; SES: socioeconomic status; FLA: Florida; NJ: New Jersey; NY: New York, PA: Pennsylvania.

61Reisch etal., 2000Medical records review/1983–1995New England HMO/n = 2,07240–6912.2% (white 84.6%; unknown 2.4%)Number of mammograms obtained over a 10-year periodMean = 3.93Mean = 4.49Significant (unadjusted) Not significant (adjusted for age, BMI, estrogen use, SES)
60Yood et al., 1999Review of radiology, billing and administrative data/1989–1996Michigan HMO/n = 8,74950–7420.8% (white 74.1% other 5.1%)bSubsequent screening within two years62.2%67.0%Significant (unadjusted and adjusted for demographics and SES)
62Evans et al., 1998Medical records review/ 1988–1993Breast screening outreach program NY State Public Health Dept./n = 9,485< 40–70+27.1%(white 45.6%; other 27.3%)One subsequent mammogram within 2–4 years Less likely to have a subsequent screeningSignificant (adjusted for demographics, SES and access to care)
56Song and Fletcher, 1998Washington State health dept. records review/ 1994–1995Washington State breast and cervical health program clinic (BCHP)/ n = 2,88840+11.7% (white 39.4%; other 48.9%)A 2nd evaluation at a (BCHP) at a) 15 months and b) 27 monthsa) 28.9%; b) 41.6%a) 29.4%; b) 46.4%Not significant (unadjusted and adjusted for demographics, SES and screening history)
53Taylor et al., 1998Mailed questionnaire/1995Inner-city women receiving primary care at a Seattle hospital/n = 34850–6935.1% (white 45.7%; other 19.2%)bOne screen in past year and planning to have another within twelve months53%51%Not significant (unadjusted)
58Miller and Champion, 1997Mailed questionnaire/?Convenience sample of church-going women/n = 1,08350+22.0%Three annual screenings17.4%22.1%Not provided
55Horton et al., 1996Telephone survey/ 1995Nationally representative sample (Mammography Attitudes and Usage Study)/n = 1,07140+?590+: Annual screenings; 40–49: biennial screenings47.7%47.4%Not significant (unadjusted)
59Pearlman et al., 1996Household interview/ 1990Nationally representative sample (National Health Interview Survey supplement)/ n = 8,96540–7514.7% (white 79.9%; Hispanic 5.4%)bHad one or two screenings on schedule and intends to continue23%28%Significant (adjusted for demogrpahics, SES, health status and practices, screening barriers)
52Lee and Vogel, 1995Survey questionnaire/ 1986–1993Texas breast screening project/n = 6,24455–843.5% (white 91.6%; Hispanic 4.9%)bAnnual screenings for 6–7 years4.2%15.1%Significant (adjusted for demographics, SES, access to care, breast cancer risks and beliefs)
62Mickey et al., 1995Household survey/ 1990Randomly selected FLA community sample/ n = 55140+100%Had a mammogram in the past year and a least one prior10.3%Not applicableNot applicable
63Whitman et al., 1991Medical records review/ 1984–1989Three public health clinics (A, B, C) on Chicago's south side/n = 70750+100%More than two screenings in past 5 yearsRepeat use by clinic: A < 1% B 4% C 7%Not applicableNot applicable
57Lerman et al., 1990Telephone survey/1988Randomly selected PA and NJ HMO and community members/ n = 91050+13 (white 85%; other 2%)Had more than one mammogram White race not a predictor of repeat screeningNot significant (unadjusted for demographics, SES, family history of breast cancer, screening encouraged by MD or family)

Table 1 presents results of studies of African American and white women who obtained repeat screening. When compared with the proportions of those who have ever or recently been screened, these data indicate that far fewer women of both races are receiving regular screenings. Among African Americans, repeat screening ranged from a low of 4.2% among those aged 55 years and over who participated in a Texas breast screening project54 to 53% of primary care patients who reported a recent mammogram and were very sure about having a future screening exam within twelve months.55 In general, studies that examined repeat screening behavior over longer time periods tended to have lower participation, whereas those examining future intentions rather than actual screening behavior reported higher proportions of women regularly screened. In comparing studies by data collection dates (Table 1), there is some evidence that repeat screening may be increasing over time. This observation is supported by the results of the Mammography Attitudes and Usage Studies (MAUS). The MAUS data collected in 1990 and 1992 found that 26% and 34%, respectively, of African American women were in compliance with screening guidelines,56 while 1995 MAUS data found that nearly 48% of women in this race/ethnic group were receiving regular mammograms.57

Whether African Americans are receiving repeat screenings with the same frequency as white women is uncertain. As shown in Table 1, among the ten studies that included data on African American and white women, four found no significant differences in repeat screening by race.55, 57–59 Conversely, somewhat fewer African Americans (17.4%) as compared with whites (22.1%) received three annual screenings in a study by Miller and Champion.60 Further, Pearlman et al.,61 Lee and Vogel,54 and Yood et al.64 found that white women were significantly more likely to engage in repeat mammography screening even after adjustment for a range of relevant factors. Reisch et al.65 also found that white women obtained more mammograms over a 10 year period than did African Americans (4.49 vs. 3.93), but this difference was not significant when adjusted for other variables. In contrast to the above findings, one study found that African Americans were more likely than whites to have a repeat screening exam.66

The above comparisons are complicated by differences in the definition of repeat screening across studies and by the different time periods covered by each study, given changes in screening behavior over time. Notwithstanding the lack of consensus across study results, it is clear that repeat mammography is currently underutilized by both African American and white women. Given that the success of screening is dependent upon (multiple) periodic examinations, the relatively low proportion of repeat screening in all women is of concern.

Mammography screening in African Americans by socioeconomic status

Although not uniformly consistent across studies, the majority of studies have found that among African American women, there is a positive correlation between mammography use and higher education and income levels.61, 67 However, as compared to white women of similar socioeconomic status (SES), some investigators have found greater use among African Americans with low income and limited education.41, 68 This suggests that programs aimed at increasing breast screening among low SES minorities may be having a positive effect.68

Improving access to mammography may not be sufficient to ensure comparable participation in screening across race/ethnic groups, however. Weinberg et al., for example, found that African Americans were less likely than white women to take advantage of a free-to-employees screening program.69 In another report, African Americans had fewer mammograms than whites for each number of primary care visits.70 Among members in two health maintenance organizations where access to care was theoretically equalized and insurance and other financial barriers to screening were minimized or eliminated, African Americans received proportionately fewer screenings than whites.64, 65 These findings highlight the importance of identifying and addressing additional barriers (e.g., psychosocial and cultural factors) that may prevent some African American women from developing a lifelong habit of regular mammography screening.

Followup of abnormal screening mammograms

Adequate followup of African American women who receive abnormal screening examinations must be provided if screening is to be effective. Few studies have been conducted on this topic, but preliminary findings suggest that a substantial proportion of low-income minority women may not receive recommended followup for abnormal exams.71 In addition, when adjusted for age and income, nonwhite race was found to predict longer time from original screening to final disposition of the case in a study by Chang et al.;72 however, McCarthy et al. did not find race to be a significant factor in followup.73 More research is needed to determine the role(s) of patient, physician, and medical system factors, and their likely interaction, in contributing to race/ethnic differences in receipt of adequate followup for abnormal mammograms.

Further work is also needed to evaluate women's understanding of the results of their screening exams. To our knowledge, only a single published study37 has looked at this issue. That study showed fairly high agreement between self-reported screening results and mammography records, although race specific findings were not presented. While not sufficient to ensure compliance with recommended followup of an abnormal exam, a woman's accurate understanding of the results of her screening mammogram is an important first step. Recognizing that sociodemographic, psychologic, and medical care factors, and perhaps the quality of the patient-physician relationship, may impact the understanding of medical test results, possible race/ethnic differences in these factors may ultimately impact the overall efficacy of screening for some women.

Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

While there has been little work in the area of assessing the prevalence of high-risk breast density patterns in African American women, we do know that such patterns likely influence the efficacy of screening mammography. Conversely, it is not clear how obesity affects the potential benefits of screening mammography, but it is known that obesity is more common in African American than in white women. In this section, we discuss both the known and the more theoretical impacts of these factors on screening mammography yield.

Breast density

Mammography, though regarded as the primary screening tool in the secondary prevention of breast cancer through early detection, has also been found to yield important information on the characteristics of breast tissue. These characteristics, discussed in the literature as mammographic parenchymal patterns and/or breast density, were first addressed by Ingleby and Gershon-Cohen74 and later by Wolfe.75 The appearance of breast tissue on mammography differs according to the breast composition: fat appears dark on film screen mammography as it is radiolucent, while epithelial and stromal tissue have greater density and thus appear light.76 Women who have mammographic densities in 60–75% of their breast tissue have a four-to six-fold increase in breast cancer risk compared with women with low density readings, as documented in a number of reviews.77–80 In addition to increasing a woman's risk of breast cancer, breast density complicates the reading of screening mammograms. Although some earlier work suggested that the sensitivity of screening mammography was not significantly compromised in dense breasts,81, 82 Mandelson et al. have recently reported that the sensitivity of mammography screening was significantly compromised (30% vs. 80%) in women with extremely dense breasts compared with women whose breasts were predominantly fatty. They further showed that the risk of a diagnosis of an interval cancer (cancer occurring between regular screenings) was more than six times higher (odds ratio [OR] 6.14, 95% confidence interval [CI] 1.95–19.4) in women with extremely dense breasts than in women with low density breasts.83

There is much to suggest that the hormonal milieu in which tumors arise may differ between the races. For example, there are race differences in reproductive variables and body weight, both of which influence endogenous estrogen levels. Similarly, there is much to suggest that breast density patterns are strongly influenced by these same hormones; for example, sex hormones influence growth factors that influence the proliferation of breast epithelium and stroma that can result in dense breasts.80 The distributions of these factors are known to vary across race/ethnic groups, suggesting one mechanism underlying race-linked differences in breast density.

There are studies that document differences in the prevalence of breast densities between white women and women of other ethnicities (Native American, Asian, Hispanic),84–86 although the relevance of these findings to African Americans is not clear. However, results from a recently published study in which a large number of African American women were included (n = 883) showed a race difference in breast density among women aged 65 years and younger after controlling for potential confounders.87 In the only other known report on the prevalence of high-risk breast density patterns in African American women, in the results of a small hospital-based study (97 African American women, 100 white women), Patterson et al. revealed no significant race difference in breast cancer cases.88 However, these investigators were unable to control for a number of variables that could have potentially obscured a true relationship. In neither study were density patterns quantitatively assessed using actual measurements of breast densities and breast area. Instead the more qualitative Breast Imaging Reporting and Data System89 classification scheme was used, and, at least in the case of the larger study, by multiple radiologists. While there are studies that suggest that there is good agreement between radiologists in assessing density using less quantitative measures,90 exact measures of density and dense area in relation to the total breast area are likely to detect what may be relatively small, but important, differences between study subjects. Thus, more studies that evaluate race/ethnic differences in breast density, preferably using quantitative measures in a standardized setting and controlling for possible confounding factors, are needed to definitively answer this research question. Information on race/ethnic specific correlates of breast density may be useful in better understanding observed race/ethnic differences in age-specific incidence rates.

In one other study that included race-specific findings with respect to breast densities in African American women, Wolfe et al. found that the radiographic measures of density were more predictive of the risk of breast cancer in African American women than in white women. White women had a breast cancer relative risk of 2.3 (P < .05) associated with denser breasts, whereas African American women had a risk of 5.2 (P < .05). While that study did not include information on race differences in the prevalence of breast densities or address possible race differences in correlates of density, it does suggest that breast densities may be of considerable importance to African American women.91

What is awkward about hypothesizing that African American women may have denser breasts than white women is the available data on the correlates of breast density, best summarized in a review by Saftlas and Szklo. Women with a later age at menarche, a later age at first birth, increased height, decreased weight, smaller breasts, positive family history, previous biopsy, or who were nulliparous, pre-menopausal, younger, did not breast feed, or used oral contraceptives were all more likely to have dense breasts.77 Of factors considered in an autopsy study by Bartow et al., older age and/or postmenopausal status were the factors that most protected against dense breasts. Obesity and large breast size were also highly significant predictors of breast radiolucency.84 Of course, many of these risk factors overlap with known risk factors for breast cancer and are less prevalent among African American women than among white women. In fact, it is thought that the relatively advantageous reproductive profile (with respect to breast cancer) generally observed for African Americans is the explanation for the lower incidence of postmenopausal breast cancer in African American women.92 However, if the greater prevalence of high risk patterns among younger African American compared with younger white women87 is confirmed in other investigations using standardized methodology and controlling for potential confounders (likely negative confounders), breast density may play a role in the higher incidence of breast cancer observed in young African American women. Furthermore, a higher prevalence of very dense breasts in young African American women could also complicate the reading of their mammograms, contributing to a delay in diagnosis and more advanced stage at diagnosis, as has been observed in SEER data.44

Obesity

It is well documented that the prevalence of obesity and even severe obesity is higher in African American women than in some other groups and, in particular, white women.93, 94 It has also been shown that obesity is positively correlated with breast size.95, 96 Here, we consider mechanisms by which obesity might influence the overall efficacy of screening mammography.

Detection.

Is it possible that the physical effects of obesity compromise the efficacy of screening mammography by decreasing the likelihood of detection? It is generally held that the increase in fatty breast tissue associated with obesity results in more radiolucent breasts,97 thus making breast cancer in obese women presumably easier to detect. However, it has been postulated that other factors related to obesity, and presumably larger breasts, may affect efficacy of screening as it exists in the current health care system.98 For instance, in a large breasted woman, it is often necessary that multiple views (more than the two standard views) be used for visualization of the entire breast. It is also necessary that large film cassettes and corresponding large grids (which reduce scatter radiation, thereby increasing image contrast and likelihood of detecting abnormalities)99 be used to evaluate larger breasts. In an analysis of self-reported survey data collected in Connecticut in 1994, 20% of all facilities offering screening mammography reported routinely not using large cassettes and corresponding large grids for women with large breasts.100 Only 64% of facilities routinely used multiple views for mammography of women with large breasts. Further, in a post-Mammography Quality Standards Act (MQSA)101 survey of these same facilities, only 71% of facilities were using multiple views for large breasted women and many were not routinely performing standard quality control procedures on the equipment used for viewing larger breasts (B.A. Jones, unpublished data). Although the MQSA, enacted in 1994, represented an important step in ensuring high quality screening services for all women, there is likely some remaining variability in quality of services nationwide. While the survey data cited above have limitations, they hint at possible mechanisms for a lower yield from screening mammography in obese women.

Hormonal.

Do the known hormonal effects of obesity influence the overall efficacy of mammography screening? Although we have outlined a hypothetical role for obesity in inhibiting the mammographic detection of tumors, the usual assumption is that obesity has an effect on the hormonal milieu in which tumors grow. Such tumors probably grow more quickly and aggressively than do tumors in women who are not obese, making them more difficult to detect with annual screening mammography. That excess adiposity, particularly in the upper body, is correlated with increased levels of bioavailable estrogen is well known.102 Mechanisms point to associations between obesity and/or upper body adiposity with decreased levels of sex hormone bonding globulin,103, 104 hyperinsulinemia, and correspondingly higher levels of insulin-like growth factor type I.105, 106

In studies that included large numbers of African American women, obesity has also been shown to be associated with larger tumors, positive lymph nodes, and later stage at diagnosis.30, 98, 107 Of relevance to this discussion, Jones et al. showed that, in multivariate analyses, 30% of the later stage at diagnosis observed in African American women relative to white women could be attributed to the greater prevalence of severe obesity in this population.98 Results from a recent analysis of data from the Carolina Breast Cancer Study basically confirmed these findings. Moorman et al. have shown that the association between stage at diagnosis and waist-to-hip ratio is even stronger than the association between obesity and disease stage,107 suggesting that upper body adiposity may be the factor that drives the observed associations between disease stage and obesity. Although neither study could definitively identify the underlying mechanism, the results of both studies suggest a hormonal, rather than detection, role for obesity in influencing stage at diagnosis.

These results contrast with a report by Reeves et al. in which mostly white women were studied. In that investigation, the association between obesity and stage of disease at diagnosis was only observed in women whose tumors were self-detected and not in women whose tumors were mammographically detected, suggesting that the efficacy of mammography screening is not affected by obesity.108 The issue is further confused by the findings of Hunt and Sickles. In that outcomes analysis of more than 88,000 consecutive mammographic examinations (again mostly in white women), increasing adiposity was associated with increasing rates of recall, biopsy, and cancer detection. On the other hand, it was also associated with increasing rates of diagnosis of interval cancers. Although the authors concluded that their findings add to the evidence of the deleterious effects of obesity on risk and progression of breast cancer,109 these results do not preclude the possibility that excess adiposity also interferes with detection, even in the case of mammographic screening. Obviously, the two mechanisms are not mutually exclusive. If obesity does interfere with detection it would likely disproportionately affect African American women because of the higher prevalence of obesity in this population.

Adequacy of Current Screening Guidelines for Young African American Women

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

More than one third (37%) of African American versus 25% of white breast cancer cases are diagnosed in women under the age of 50 years.23, 110 While breast cancer death in any young woman is particularly troubling, the race difference here is striking, with more than 17% of breast cancer deaths in African American women occurring in the 20–39 years old age group, compared with less than 10% in white women (SEER data, 1983–1989).111 More recent age-adjusted data from the SEER program (1989–1996) show that African American women continue to be diagnosed with more advanced stage of disease and have lower five-year relative survival rates within each stage category than do white women.4 This race difference in stage at diagnosis is seen in younger women as well, with only 47% of African American women, compared with 56% of white women, under the age of 50 years presenting with localized cancers.44

Because of the earlier age at diagnosis and poorer outcome in young African American women, the question of efficacy of screening mammography in women under the age of 50 years is quite relevant. While the results of a number of randomized clinical trials have shown a clear reduction in breast cancer mortality with mammography screening in women over the age of 50 years, the benefit in younger women has been debated.2, 10 However the results of a recent meta-analysis of randomized clinical trials that included women in the 40–49 years old age group showed significantly lower mortality rates in mammography screened women than in the control groups.3 In spite of the reduced mortality, a study that evaluated the sensitivity of modern screening mammography by decade of age in a diverse population (36% nonwhite) showed that the sensitivity of mammography to detect invasive breast cancer was still lower among women aged 40–49 years compared with women aged 50 years or older (75% versus 92%).82 Sickles has shown that for women in this younger age group, the sensitivity of screening mammography decreases from 87 percent with a one year interval to 73 percent with a two year interval between screenings.107

It has been suggested that the lower sensitivity for women aged 40–49 years compared to older women may result from the more radiographically dense breasts observed in younger women.113 An alternative explanation for the lower screening sensitivity for younger women (aged 40–49 years) is that the rapid tumor growth rates in younger women result in the diagnosis of interval cancers. Indeed, the results of one study now suggest that African American women, particularly those under the age of 65 years, may have a higher prevalence of dense breasts than observed in other groups.87 Yet there is also mounting evidence that breast cancer in African American women may be biologically more aggressive than in white women.114, 115 In addition to tumor characteristics associated with poorer prognosis (e.g., estrogen receptor negative tumors), there may be other factors that are more prevalent among African American women and that may also contribute to more aggressive disease (e.g., obesity). More research is needed in the area of understanding tumor biology in younger African American women. The impact of these biologic variables on screening efficacy should be considered in a discussion of optimal screening guidelines for African American women.

It is known that there is significant benefit associated with repeat mammography. Sickles showed that the benefit is seen in younger women as well as older women. Significant improvement in size and stage at the time of diagnosis is evident from the evaluation of a large screening program in which tumors diagnosed at an initial screening were compared with tumors diagnosed at a subsequent screening. While there is a similar benefit shown in older women, in women aged 40–49 years, the average tumor size decreased from 14 millimeters to 10 millimeters, the proportion of tumors with nodal metastasis decreased from 17% to 13%, and the proportion of tumors Stage II or higher decreased from 24% to 16%. Notwithstanding some of the concerns about efficacy in younger women, these results suggest that young women benefit from repeat screening at least with respect to stage at diagnosis.112

One potential but as yet unstudied benefit to beginning screening mammography at early ages would be a beneficial effect on the rates of repeat screening. These rates are low in all women, including African Americans. Presumably, as women approach a significant age benchmark, 40 years, obtaining annual screening mammograms may not be a top priority. In fact, it may take several years before women get into the habit of annual screening mammograms. This may be an even more significant issue for women of low socioeconomic status who have many competing demands in their lives. To the extent that African American women are more likely to be socioeconomically disadvantaged than their white counterparts, this might contribute to lower repeat screening rates in this population.

Recommendation

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

Although breast cancer in young African American women is recognized as a growing public health concern, it remains a relatively rare event. Thus, any recommendation for shorter intervals or earlier age at which to begin screening must be balanced with a complete understanding of the potential adverse effects. As has been discussed by others,116 screening younger women can be problematic, with reduced sensitivity and specificity. False negative exams can result in false assurance to some women, perhaps deterring future screening, while false positive tests involve both human costs (e.g., psychologic distress, risk associated with diagnostic procedures) and financial costs (e.g., unnecessary biopsies).

To guard against a high number of false positive screening tests, any strategy for screening younger women should require that only high-risk women be targeted. At this time, this strategy would be difficult to implement, as our understanding of the etiology, including specific genetic markers, of breast cancer in very young African American women is not well understood. While models have been developed to assess a woman's risk for breast cancer,117, 118 these were based on study populations composed of primarily white women and therefore may be inadequate for targeting high-risk young African American women. And finally, there is the possibility that a high-risk label by virtue of race/ethnicity (and age) could negatively impact a woman's psychologic well-being, as well as her insurability and employment opportunities.

Although it has been suggested by some that African American women might benefit from mammographic screening that begins before the age of 40 years, at this time there is not enough evidence that the benefits would outweigh the risks. Currently, the best strategy is to continue to promote screening mammography in all women according to established guidelines. African American women should be screened annually beginning at age 40, with special efforts made to encourage regular screening in accordance with recommended intervals. Other screening modalities are under development and may be useful in younger high-risk women. Research efforts directed toward the development of new technologies that may be used to identify premalignant lesions, such as nipple aspirate and ductal lavage, may be particularly important for young African American women.

DISCUSSION

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

While there is little reason to doubt the early detection benefits of mammography when delivered under optimal conditions (as in a clinical trial setting), the results of some observational data suggest that there may be barriers that diminish the actual efficacy of this screening test for African American women in our current health care system. Despite recent improvements in earlier diagnosis and survival from breast cancer for all women, SEER data still show significant race gaps in outcome with respect to stage at diagnosis and survival from breast cancer (SEER five-year relative survival rates, 1989–1995: whites 86% vs. blacks 71%).4 Although some lag between more screening and improved outcomes would be expected, these disparities have persisted into the years in which more African American women are receiving mammograms. One possible contributing factor to a persistent race gap even when mammography screening increases is that there is a distinction between offering mammography in the highly controlled and standardized setting of a clinical trial versus the actual field setting. That is, the real efficacy of screening mammography requires that women receive high quality exams, receive timely notification of their results, understand their results, comply with suggested followup for abnormal exams, and return for subsequent screening at recommended intervals. To the extent that we know relatively little about race differences in these process variables, we can only speculate that variation in these factors may contribute to a lower mammography efficacy for some women and may have a differential impact across race/ethnic groups.

The proportions of African American women who have undergone one-time or recent screening now appear comparable to the proportions in white women, according to national surveys. However, some studies suggest that race disparities in mammography screening persist in some areas of the country. While mammography rates should continue to be monitored, additional research is needed to determine if African Americans receive repeat screenings as often as white women do. Although the data are not clear on this point, it is apparent that repeat screening, which is needed to effectively reduce breast cancer mortality, is currently underutilized by both African American and white women. African Americans must be included in sufficient numbers in such investigations so that barriers unique to this population can be identified. At this time, research should be conducted that identifies factors that promote (and hinder) a lifelong habit of mammography screening.

Because the full benefit of mammography screening is dependent not only on receiving regular screening but also upon receiving high quality mammograms, there should be continued efforts to monitor compliance with regulations promulgated by the Mammography Quality Standards Act.101 In the only study to our knowledge that has addressed the question of race-linked variability in quality of services, the results of a Connecticut-based study conducted before implementation of the MQSA showed that African American women were not more likely than others to receive their mammograms from facilities that offered substandard services.100 While these results were encouraging, they were based on self-reported data from mammography facilities, most of which could only estimate the proportion of their clientele that was African American. With the development of mammography registries and large ongoing screening programs such as the NBCCEDP in which race/ethnic information is recorded, there will be better opportunities to evaluate these and other questions in a more meaningful way.

A better understanding of the potential impact of ethnic variation in patient characteristics on screening mammography yield is also needed. More research on potential race differences in prevalence of high-risk density patterns and race specific correlates of high-risk patterns would help clarify whether this is an added risk for African American women, particularly at young ages.

While obesity is generally associated with more radiolucent breasts, it is also associated with an increase in interval cancers109 and later stage at diagnosis of breast cancer.98, 107 Thus, the deleterious effects of obesity on circulating levels of hormones and tumor progression may outweigh the beneficial effects of obesity on the composition of breast tissue in enabling detection. It is possible that the current recommendations regarding screening intervals are not adequate for obese women. To the extent that obesity is not uncommon in African American women and seems to be on the rise in young African American women in particular, the potential for obesity to interfere with the efficacy of screening mammography must be explored further.

According to national surveys, the proportions of African-American women who have undergone one-time or recent screening now appear comparable to the proportions of white women, although some studies suggest that race disparities in one-time screening persist in some areas of the country. While one-time use and recent screening should continue to be monitored nationally and at the state level, additional research is neeeded to determine if African-Americans receive repeat screenings as often as white women.

Finally, we offer the comment that one potential barrier to mammography screening and participation in studies of mammography screening is an uneasiness with the health care system and the research establishment among some African American women. While the factors that contribute to this uneasiness are not easily studied, they may include distrust, perceived discrimination, or perceived lack of equality with other patients.119–121 It is therefore recommended that all research requiring the participation of African American women be conducted in a culturally sensitive manner. This should apply to all aspects of research, including the recruitment of study subjects, obtaining informed consent, the conduct of interviews and/or interventions, and followup or evaluation. Useful strategies include but are not limited to the following: community endorsement and participation in the planning and implementation of a research initiative; the use of culturally sensitive language in interview instruments; participation of African American researchers, interviewers, and project managers; and the involvement of African Americans in focus groups used to identify unique cultural dynamics.

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES

Notwithstanding some controversy8, 9 regarding the benefits of screening mammography, it is generally assumed that the effects are the same for women of all race/ethnic groups. Yet, the evidence from clinical trial data is derived almost exclusively from the study of white women. By studying race specific processes and characteristics, we can build on this rich body of knowledge to achieve maximum benefit in African American women. In the current review, we have discussed a number of factors that may affect the efficacy of this screening strategy as it is delivered in the current health care system, particularly process of care factors that may affect repeat screening and/or receipt of appropriate followup after abnormal exams. From a more theoretical perspective we have identified factors that may impact the benefit of screening mammography in African Americans because those factors may be distributed differently across race/ethnic groups, specifically, obesity and high-risk breast density patterns. More research is needed in these areas as well. The present need is for a screening modality effective in all African American women, and particularly for younger women, who are disproportionately burdened in terms of incidence, morbidity, and mortality. Until new strategies are available that can identify premalignant lesions, screening mammography remains the best tool available, and the current guidelines seem appropriate to reduce the diagnosis of advanced breast cancer in African American women.

REFERENCES

  1. Top of page
  2. Abstract
  3. Evidence for the Efficacy of Screening Mammography in African American Women from Clinical Trials and Observational Studies
  4. Receipt of Screening Mammograms Among African Americans
  5. Potential Impact on Screening Mammography Yield of Race and Ethnic Variation in Breast Density and Obesity
  6. Adequacy of Current Screening Guidelines for Young African American Women
  7. Recommendation
  8. DISCUSSION
  9. CONCLUSIONS
  10. Acknowledgements
  11. REFERENCES