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Keywords:

  • cancer;
  • socioeconomic status;
  • racial disparities;
  • treatment;
  • survival

Abstract

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONFLICT OF INTEREST DISCLOSURES
  7. REFERENCES

BACKGROUND:

This is the first study to use the linked National Longitudinal Mortality Study and Surveillance, Epidemiology, and End Results (SEER) data to determine the effects of individual-level socioeconomic factors (health insurance, education, income, and poverty status) on racial disparities in receiving treatment and in survival.

METHODS:

This study included 13,234 cases diagnosed with the 8 most common types of cancer (female breast, colorectal, prostate, lung and bronchus, uterine cervix, ovarian, melanoma, and urinary bladder) at age ≥25 years, identified from the National Longitudinal Mortality Study-SEER data during 1973 to 2003. Kaplan-Meier methods and Cox regression models were used for survival analysis.

RESULTS:

Three-year all-cause observed survival for cases diagnosed with local-stage cancers of the 8 leading tumors combined was ≥82% regardless of race/ethnicity. More favorable survival was associated with higher socioeconomic status. Compared with whites, blacks were less likely to receive first-course cancer-directed surgery, perhaps reflecting a less favorable stage distribution at diagnosis. Hazard ratio (HR) for cancer-specific mortality was significantly higher among blacks compared with whites (HR, 1.2; 95% confidence interval [CI], 1.1-1.3) after adjusting for age, sex, and tumor stage, but not after further controlling for socioeconomic factors and treatment (HR, 1.0; 95% CI, 0.9-1.1). HRs for all-cause mortality among patients with breast cancer and for cancer-specific mortality in patients with prostate cancer were significantly higher for blacks compared with whites after adjusting for socioeconomic factors, treatment, and patient and tumor characteristics.

CONCLUSIONS:

Favorable survival was associated with higher socioeconomic status. Racial disparities in survival persisted after adjusting for individual-level socioeconomic factors and treatment for patients with breast and prostate cancer. Cancer 2011. © 2011 American Cancer Society.

Racial/ethnic disparities in healthcare and outcomes have been evident for almost all cancer sites as indicated by the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Annual Cancer Statistics Review,1 cancer facts and figures presented by the American Cancer Society,2 and other studies.3-20 For example, the annual review of the 1973 to 2007 data showed that blacks had a higher mortality for breast, colorectal, lung, prostate, and many other common tumors than whites.1 The increased mortality in blacks with cancer can be attributed to more aggressive cancers and more advanced stage at diagnosis,1, 2, 20 differences in treatment,10-13 socioeconomic factors,8, 10-13 physician characteristics,9 and personal beliefs.21 There have been numerous original studies and meta-analyses on racial disparities in survival, and the results are not consistent.11-13 Some studies demonstrated that if patients had equal access to quality healthcare, the outcomes would be similar among different racial groups.10-13 However, other studies showed that racial disparities still existed even after controlling for socioeconomic factors and for access to equitable care and treatment.10-13

Many of these studies examined 1 or several specific tumor sites, and few studies reported all or multiple tumor sites from the same cohorts of population on racial disparities in survival, treatment, and socioeconomic factors. This study presents the recently linked data between the 30 cohorts of the National Longitudinal Mortality Study and SEER cancer registries. We aimed to determine the effect of socioeconomic factors at the individual level (ie, health insurance, education, income, and poverty) on racial disparities in receiving treatment and in survival among patients diagnosed with cancer. This study examined racial disparities for 8 specific types of tumor and also for all 8 tumors combined. We hypothesized that patients with no insurance or with lower socioeconomic status (SES) were less likely to receive the recommended therapy compared with those with private health insurance and those with higher SES, and that racial disparities in treatment were largely explained by differences in health insurance status and socioeconomic factors. We also hypothesized that patients with no insurance or with lower SES would experience less favorable survival (all-cause and cancer-specific) compared with those with private health insurance and higher SES and that racial disparities in survival were largely explained by differences in health insurance, SES, and treatment rendered.

MATERIALS AND METHODS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONFLICT OF INTEREST DISCLOSURES
  7. REFERENCES

Data Sources and Study Population

This study used the SEER-National Longitudinal Mortality Study linked data for cases in 15 participating SEER registries between 1973 and 2003. The detailed methods for this data linkage were described elsewhere.20, 22, 23 In brief, the SEER-National Longitudinal Mortality Study linkage was conducted by the Census Bureau, and the linked dataset is maintained by the Census Bureau in compliance with registry and federal requirements to protect health information of human research subjects.

The SEER registries ascertain all newly diagnosed incident invasive cancer cases from multiple reporting sources.24 Information includes tumor location, stage, size, and grade; demographic characteristics such as age, sex, race, and marital status; and types of first course treatment provided within 4 to 6 months after the date of diagnosis. The National Longitudinal Mortality Study is an ongoing mortality follow-up study of selected cohorts from the Census Bureau's Current Population Survey respondents and Census sample. To date, the 30 cohorts in the National Longitudinal Mortality Study were sampled and surveyed in March 1973, 1979, and 1981 through 2003, with additional surveys in February 1978, April, August, and December 1980, and September 1985, as well as the 1980 Census E Sample. We studied the 8 most common tumors (breast, colorectal, prostate, lung and bronchus, cervix, ovarian, melanoma of the skin, and urinary bladder cancer) because of relatively large numbers of cases that provided informative results for most stratified analyses by race/ethnicity and SES.

All cases were diagnosed with a primary malignant cancer in 1 of 15 SEER registries. Years of cancer diagnosis varied across registries. In the SEER 9 registries (San Francisco Bay Area, Connecticut, Metropolitan Detroit, Hawaii, Iowa, New Mexico, Seattle [Puget Sound], Utah, and Metropolitan Atlanta), cases were diagnosed from 1979 through 2003. In the San Jose-Monterey and Los Angeles registries, cases were diagnosed from 1992 through 2003. In the Greater California, Kentucky, Louisiana, and New Jersey registries, cases were diagnosed from 2000 through 2003. A total of 13,620 cases met National Longitudinal Mortality Study requirements for matching to the National Death Index and were 25 years of age or older at the time of their Current Population Survey. Of these cases, 386 were excluded from analysis because of incomplete racial and ethnicity data, resulting in an analytic dataset of 13,234 cases.

Sociodemographics

Race/ethnicity was classified into non-Hispanic white, non-Hispanic black, non-Hispanic Asian or Pacific Islander, Hispanic, and American-Indian or Alaskan-Native. Age at diagnosis was categorized in 10-year intervals. Socioeconomic variables included health insurance, years of education, family income, and poverty status. Health insurance was originally categorized into employer healthcare, government, Medicare, private company, Medicaid, uninsured, and unknown or missing. Education was classified into less than high school (<12 years), high school graduate (12 years), and some education after high school (≥13 years). There were 3 cases with missing information on education that were not reported in the results. Family income referred to total combined income of all family members during the 12 months preceding the survey,20 and the dollar amount or the median value of the category of income was adjusted to the year 1990 dollars by the appropriate consumer price index value for inflation in individuals from various National Longitudinal Mortality Study cohorts. We categorized the family income as <$10,000, $10,000 to $34,999, ≥$35,000, and unknown/missing. Poverty status was measured as of the 1990 census in terms of the ratio of the family income to the poverty threshold for a 4-person family20 and grouped into ≤100% (lowest), 100% to 400%, ≥400%, and unknown or missing.

Tumor Characteristics and Treatment

Tumor characteristics and treatment variables were obtained from the SEER data. The 8 common tumor sites included breast (female), colorectal, prostate, lung and bronchus, cervix, ovarian, melanoma of the skin, and urinary bladder cancer. Because we included cases with cancer from 1979 through 2003, SEER historic tumor stages were analyzed rather than the American Joint Committee on Cancer Stage, which has been available since 1988. First-course cancer-directed surgery was defined according to the SEER surgery codes, mostly those with codes of >10. Specific codes for common tumor sites included: breast (10-90), colorectal (30-90), prostate (20-90), lung and bronchus (30-90), cervical (20-90), ovarian (10-90), melanoma of the skin (20-90), and urinary bladder (10-90). First-course radiation therapy was defined from the SEER variable “radiation therapy” as yes or no.

Survival

The observed survival time in months was calculated from the date of cancer diagnosis to the date of death or to the date of last follow-up (December 31, 2003). All-cause mortality was defined as death from any cause as provided in the SEER registry data. Patients still alive at the last date of follow-up were censored. The cancer-specific mortality was defined as cancer (of any type) being the underlying cause of death. In this specific analysis, patients who died of causes other than cancer or were still alive at the date of last follow-up were censored. The 3-year observed survival rate was calculated as the proportion of patients who survived for at least 3 years among those cases who were followed up for at least 3 years after the date of cancer diagnosis using the Kaplan-Meier product limit methods.

Analysis

All analyses were weighted according to data size, number of cohorts, and US populations during the study period. Differences in the distribution of baseline characteristics among the racial/ethnic groups were tested using the chi-square statistic. Multivariate logistic regression analyses were used to assess the odds ratio of receiving various therapies in association with race/ethnicity while adjusting for age, sex, and tumor stage, and by further adjusting for socioeconomic variables (education, family income, and poverty status) and health insurance in those without missing data for health insurance. In the Cox proportional hazard regression analyses of survival, the hazard ratio of all-cause or cancer-specific mortality was presented with race/ethnicity in the models while adjusting for age, sex, and tumor stage, and by further adjusting for socioeconomic variables (education, family income, and poverty status), treatment (cancer-directed surgery and radiation therapy), and health insurance in those with usable data for health insurance.

RESULTS

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONFLICT OF INTEREST DISCLOSURES
  7. REFERENCES

Table 1 presents the distribution of patient age, sex, tumor stage, and SES (health insurance, years of education, family income, and poverty status) among racial/ethnic groups of patients diagnosed with the 8 most common types of cancer. A higher proportion of cases were diagnosed at age <45 among Hispanics (5.9%) compared with non-Hispanic whites (4.0%). A slightly higher proportion of cases were men than women. A larger proportion of black cases were diagnosed with distant stage cancer, whereas greater percentages of cases were diagnosed with localized stage among whites and among Asians and Pacific Islanders. A greater proportion of non-Hispanic blacks, American-Indians and Alaska-Natives, and Hispanics had Medicaid coverage or no health insurance, whereas a higher percentages of Asian and white patients had employer or private healthcare. Larger proportions of black and Hispanic cases were in the lowest categories of educational attainment, family income, and poverty status compared with whites. For example, 44.5% of Blacks and 52.4% of Hispanics had less than a high school diploma compared with 23.6% of whites. The differences in the distribution of the above factors between ethnic groups were all statistically significant.

Table 1. Comparison of Demographic and Tumor Characteristics by Race/Ethnicity
CharacteristicsNH-WhiteNH-BlackNH-APIHispanicAI/AN
No.%No.%No.%No.%No.%
  • NH indicates non-Hispanic; API, Asian/Pacific Islander; AI/AN, American Indian/Alaska Native.

  • To avoid any cell with n < 16 (Surveillance, Epidemiology, and End Results [SEER] data user agreement), government health insurance was combined with employer category for Table 1 only; cases with missing information for education and cases with n < 16 for AI/AN were not reported.

  • a

    For prostate cancer, localized/regional stages were combined in SEER and were reported here as localized stage.

Age, y          
 <454254.0303.3375.5495.9
 45-54122011.311912.97511.110913.0
 55-64233021.726628.913820.419423.2
 65-74345132.129431.921732.029234.9
 75-84258124.017519.016924.915118.1
 85+7426.9384.1426.2414.9
Sex          
 Men576753.750755.034651.045654.52551.0
 Women498246.341545.033249.038045.52449.0
Tumor stage          
 Localizeda364533.921223.024936.723928.6
 Regional239822.319120.716424.219122.8
 Distant165915.419320.911517.013516.1
 Localized/regional (prostate)223820.824626.712718.721926.2
 Unstaged/missing8097.5808.7233.4526.2
Health insurance          
 Employer/Medicare/private/government460442.834334.232948.537344.62449.0
 Medicaid/not Insured4694.4667.2436.310812.9
 Unknown567652.851355.630645.135542.5
Years of education          
 <12253823.641044.519628.943852.42551.0
 12405037.726328.525036.923928.6
 ≥13415838.724927.023234.215919.0
Family income quintile          
 <$10,0008788.219320.9558.114417.21836.7
 $10,000-$34,999391936.537340.523334.438145.6
 ≥$35000536549.930232.836353.527032.3
 Unknown5875.5545.9274.0414.9
Poverty status quintile          
 ≤100%6185.716217.6588.615218.21734.7
 100%-400%483345.046750.731746.845654.51734.7
 ≥400%429740.021122.928642.216820.1
 Unknown10019.3828.9172.5607.2
 Total1074910092210067810083610049100

Table 2 presents the percentage of cases receiving first course of cancer-directed surgery and radiation therapy by tumor stage, ethnicity, and SES. A slightly larger proportion of white and Asian and Pacific Islander cases with local stage tumors received cancer-directed surgery compared with Hispanics and blacks. Receipt of surgery declined for all racial and ethnic groups among those with distant stage cancer. The receipt of cancer-directed surgery and radiotherapy was generally higher among those with employer or private insurance or Medicare and those with more education, and lower among those with Medicaid or no insurance and those with less education. Receipt of surgery and radiation varied across sites, reflecting the unique clinical feature of each tumor site.

Table 2. Percentage of Cases Receiving Surgery and Radiotherapy by Race and SES Stratified by Tumor Stage
CharacteristicLocalRegionalLocal/Regional (Prostate)Distant
SurgeryRadiationSurgeryRadiationSurgeryRadiationSurgeryRadiation
  • SES indicates socioeconomic status; NH, non-Hispanic; API, Asian/Pacific Islander; AI/AN, American Indian/Alaska Native.

  • a

    Not reported for 3 cases with missing education.

  • b

    For prostate cancer, localized/regional stages were combined in Surveillance, Epidemiology, and End Results and were reported here as localized stage.

Race/ethnicity        
 NH-white80.720.067.333.933.435.129.132.1
 NH-black77.822.658.638.733.330.523.831.1
 NH-API82.325.373.236.626.847.231.332.2
 Hispanic77.025.973.336.138.426.640.725.9
 AI/AN76.938.560.033.318.245.550.012.5
Health insurance        
 Employer/Medicare/private78.922.765.835.131.235.127.631.4
 Government72.25.673.917.433.327.814.350
 Medicaid/not insured74.422.863.734.729.333.325.936.7
 Unknown82.519.169.034.235.734.231.730.7
Years of educationa       
 <1277.617.161.331.225.430.627.730.6
 1280.319.566.136.831.837.229.136.9
 ≥1382.224.374.534.538.734.832.234.7
Tumor sites        
 Breast88.840.491.338.1  52.437.4
 Colorectal70.06.091.115.5  64.513.2
 Prostateb    33.434.64.118.7
 Lung and bronchus46.521.720.649.2  3.549.7
 Cervix78.630.836.492.7  16.755.6
 Ovarian94.00.081.80.0  71.41.5
 Melanoma of the skin87.60.874.53.9  45.025
 Urinary bladder85.01.884.524.2  61.523.1

Table 3 presents survival rates by racial/ethnic groups, SES, and tumor sites. The overall observed 3-year survival for all cases with local stage tumor was 85% for whites, 82% for blacks, 85% for Asian and Pacific Islanders, 90% for Hispanics, and 86% for American Indians/Alaska Natives. As expected, the survival rate was lower for advanced stage tumors, but the general patterns by ethnicity were similar for all-cause and for cancer-specific survival. More favorable survival was experienced by patients with health insurance and higher education compared with cases without health insurance and lower education. Percentage of 3-year observed survival was relatively high among those with melanoma or breast or prostate cancer, and low among cases with lung cancer. The survival rate was high for those with early stage cervical and ovarian cancer, but low among those diagnosed with late stage cancer of these sites.

Table 3. Observed 3-Year Survival Rate by Race and SES Stratified by Tumor Stage
CharacteristicObserved 3-Year Survival Rate (95% CI)
Local StageRegional StageDistant StageUnstaged/Missing
All- CauseCancer- SpecificAll- CauseCancer- SpecificAll- CauseCancer- SpecificAll- CauseCancer- Specific
  • SES indicates socioeconomic status; CI, confidence interval; NH, non-Hispanic; API, Asian/Pacific Islander; AI/AN, American Indian/Alaska Native.

  • a

    Not reported for 3 cases with missing education.

  • b

    For prostate cancer, localized/regional stages were combined in SEER and were reported here as localized stage.

Race/ethnicity        
 NH-white85 (84-86)92 (91-93)49 (47-52)55 (53-57)13 (11-15)14 (12-16)36 (33-39)42 (39-46)
 NH-black82 (79-86)88 (85-91)42 (35-49)47 (40-54)16 (11-20)17 (12-22)37 (27-47)44 (33-55)
 NH-API85 (80-89)91 (87-95)59 (49-68)64 (54-74)20 (11-30)23 (13-33)34 (12-56)45 (18-72)
 Hispanic90 (86-93)94 (91-97)54 (45-63)62 (52-71)14 (7-22)15 (8-23)39 (23-55)43 (26-60)
 AI/AN86 (68-100)94 (82-100)26 (3-50)28 (3-53)0021 (0-100)21 (0-100)
Health insurance        
 Employer/Medicare/private85 (83-86)92 (91-93)50 (47-53)55 (52-58)14 (12-16)15 (12-17)38 (32-43)44 (38-50)
 Government83 (69-97)84 (71-98)42 (19-65)51 (25-76)0000
 Medicaid/not insured76 (70-81)85 (80-90)47 (40-55)51 (43-59)8 (3-12)9 (4-14)29 (14-44)33 (16-50)
 Unknown85 (84-87)93 (92-93)49 (46-52)55 (52-58)14 (12-16)15 (13-18)36 (32-40)43 (38-47)
Years of educationa        
 <1274 (72-77)85 (83-87)39 (35-42)44 (40-47)10 (7-12)11 (8-13)31 (27-36)38 (32-43)
 1285 (84-87)92 (91-93)49 (46-52)55 (52-58)13 (11-16)14 (11-16)40 (34-45)46 (40-52)
 ≥1390 (89-91)95 (95-96)59 (56-62)65 (61-68)18 (15-21)20 (16-23)39 (33-45)46 (40-53)
Tumor sites        
 Breast90 (89-92)96 (95-97)82 (80-85)88 (86-90)29 (22-36)32 (24-40)48 (37-59)63 (51-76)
 Colorectal81 (78-84)91 (88-93)60 (57-64)67 (63-70)11 (8-14)12 (9-15)33 (24-42)40 (30-50)
 Prostateb89 (88-91)96 (95-96)37 (30-44)41 (34-48)63 (57-68)76 (70-81)
 Lung and bronchus43 (38-48)49 (44-55)15 (13-17)17 (14-19)3 (2-4)3 (2-4)10 (7-13)11 (8-15)
 Cervix89 (81-97)93 (87-100)59 (45-74)63 (51-78)12 (0-26)12 (0-26)50 (14-86)56 (19-94)
 Ovarian88 (80-96)94 (88-100)74 (54-95)74 (49-77)34 (28-39)37 (30-43)22 (4-39)24 (6-43)
 Melanoma of the skin91 (89-94)96 (94-98)49 (34-65)56 (39-73)8 (0-22)9 (0-23)90 (75-100)93 (81-100)
 Urinary bladder78 (75-81)89 (86-92)28 (21-35)37 (28-46)9 (0-20)10 (0-22)65 (48-83)74 (56-91)

Table 4 presents results of the multivariate logistic regression analysis for receiving cancer-directed surgery and radiation therapy by socioeconomic attributes and by tumor site. Black cases were less likely to receive cancer-directed surgery than whites, even after controlling for education, income, and poverty status at the individual level in addition to other patient and tumor characteristics (odds ratio, 0.7; 95% confidence interval [CI], 0.6-0.8) and further adjusting for health insurance (odds ratio, 0.5; 95% CI, 0.4-0.6). There were no significant differences among ethnic groups for receiving radiation therapy after adjusting for socioeconomic factors. The results were similar in tumor site-specific analyses, but the CIs were wider because of smaller samples.

Table 4. Receipt of Cancer-Directed Surgery and Radiation Therapy by Tumor Site and Race
Cancer SiteRace/EthnicityCancer-Directed SurgeryRadiotherapy
Model 1, n=13,234Model 2, n=6367Model 1, n=13,234Model 2, n=6367
No.OR (95% CI)No.OR (95% CI)OR (95% CI)OR (95% CI)
  1. OR indicates odds ratio; CI, confidence interval; NH, non-Hispanic; Ref, reference; API, Asian/Pacific Islander; AI/AN, American Indian/Alaska Native.

  2. To avoid any cell with n < 16 (Surveillance, Epidemiology, and End Results data user agreement), cervical cancer and melanoma were not reported, cases with n < 20 were reported for NH-black and NH-API with ovarian and urinary bladder cancer.

  3. Model 1: Hazard ratio adjusted for age, sex, tumor stage, education, poverty, and family income. Model 2: Hazard ratio additionally adjusted for health insurance in subjects with data on health insurance.

All 8 cancers combinedNH-white10,7491.0 Ref50731.0 Ref1.0 Ref1.0 Ref
NH-black9220.7 (0.6-0.8)4090.5 (0.4-0.6)1.0 (0.8-1.2)1.1 (0.9-1.5)
NH-API6781.1 (0.9-1.4)3721.2 (0.9-1.7)1.1 (0.9-1.4)1.2 (0.9-1.6)
Hispanic8361.1 (0.9-1.3)4811.1 (0.8-1.3)1.0 (0.8-1.2)1.1 (0.8-1.4)
AI/AN490.9 (0.4-1.9)320.9 (0.4-2.2)0.8 (0.3-1.7)0.8 (0.3-2.1)
BreastNH-white24921.0 Ref11691.0 Ref1.0 Ref1.0 Ref
NH-black2140.7 (0.5-1.2)860.7 (0.3-1.3)0.7 (0.5-1.0)0.8 (0.4-1.3)
NH-API1911.3 (0.6-2.7)1152.0 (0.8-5.1)1.0 (0.7-1.5)1.1 (0.7-1.8)
Hispanic2160.9 (0.5-1.5)1291.5 (0.8-2.7)1.2 (0.9-1.7)1.2 (0.8-2.0)
ColorectalNH-white17911.0 Ref7911.0 Ref1.0 Ref1.0 Ref
NH-black1400.7 (0.5-1.1)560.5 (0.3-1.0)0.9 (0.5-1.5)0.6 (0.2-1.5)
NH-API1451.0 (0.6-1.7)751.2 (0.6-2.3)1.1 (0.6-2.1)1.3 (0.6-3.4)
Hispanic1660.5 (0.3-0.8)980.6 (0.3-1.0)1.7 (1.0-3.0)1.7 (0.7-3.9)
ProstateNH-white26521.0 Ref12321.0 Ref1.0 Ref1.0 Ref
NH-black3110.8 (0.6-1.1)1370.7 (0.4-1.1)0.8 (0.6-1.1)1.0 (0.6-1.6)
NH-API1520.8 (0.5-1.3)800.8 (0.4-1.5)1.4 (0.9-2.2)1.5 (0.9-2.8)
Hispanic2521.3 (0.9-1.9)1320.9 (0.5-1.5)0.7 (0.5-1.0)1.1 (0.7-1.8)
Lung and bronchusNH-white22411.0 Ref10571.0 Ref1.0 Ref1.0 Ref
NH-black2070.8 (0.5-1.3)1010.5 (0.2-1.1)1.0 (0.7-1.3)1.4 (0.8-2.2)
NH-API1262.0 (1.1-3.6)691.8 (0.8-4.0)0.9 (0.6-1.5)1.0 (0.6-1.9)
Hispanic1251.5 (0.8-3.5)691.0 (0.4-2.2)0.7 (0.6-1.5)0.7 (0.4-1.3)
OvarianNH-white3181.0 Ref1431.0 Ref1.0 Ref1.0 Ref
NH-black290.9 (0.3-2.4)<200.6 (0.1-2.8)UndefinedUndefined
NH-API175.3 (0.8-35.0)<205.1 (0.4-72.4)10.6 (1.3-87.1)Undefined
Hispanic382.4 (0.8-6.8)2115.3 (1.0-225)5.5 (0.2-198.0)4.0 (0.1-291.9)
Urinary bladderNH-white7951.0 Ref3951.0 Ref1.0 Ref1.0 Ref
NH-black290.5 (0.2-1.3)<200.7 (0.1-4.2)0.5 (0.1-2.1)1.6 (0.3-10.2)
NH-API382.0 (0.8-5.2)<202.2 (0.5-9.1)0.30 (0.1-1.3)Undefined
Hispanic341.9 (0.4-9.3)201.0 (0.2-5.1)0.4 (0.1-1.6)0.6 (0.1-3.8)

Table 5 presents the effect of race/ethnicity, socioeconomic factors, and treatment on all-cause and cancer-specific mortality while adjusting for other patient and tumor factors. In an initial model that compared with whites, blacks were significantly more likely to die of cancer after adjusting for age, sex, and tumor stage (hazard ratio, 1.2; 95% CI, 1.1-1.3). The statistical significance of the hazard ratio of cancer-specific mortality was no longer elevated for blacks compared with whites (hazard ratio, 1.0; 95% CI, 0.9-1.1) after further controlling for socioeconomic factors (education, income, and poverty status) and treatment. Hazard ratios for cancer-specific mortality among blacks were similar to those for all-cause mortality. Asian and Pacific Islanders and Hispanics appeared to have lower risk of all-cause and disease-specific mortality, whereas mortality among American Indians and Alaska Natives was elevated but not significantly different from that in whites after controlling for patient and tumor characteristics, treatment, education, income, and health insurance. We also added the registry variable (15 locations) to the final model and found that the hazard ratio of all-cause mortality among blacks compared with whites was essentially unchanged (hazard ratio, 1.03; 95% CI, 0.94-1.11).

Table 5. Hazard Ratios of Mortality by Race/Ethnicity Among Patients With Invasive Tumors
CharacteristicHazard Ratio (95% CI) of All-Cause MortalityHazard Ratio (95% CI) of Cancer-Specific Mortality
No.Model 1No.Model 2Model 1Model 2
  1. CI indicates confidence interval; NH, non-Hispanic; Ref, reference; API, Asian/Pacific Islander; AI/AN, American Indian/Alaska Native.

  2. Model 1: Hazard ratio adjusted for age, sex, tumor stage, education, poverty, family income, surgery, and radiotherapy. Model 2: Additionally adjusted for health insurance in cases with these data, in addition to above variables.

Race/ethnicity      
 NH-white10,7491.0 Ref50731.0 Ref1.0 Ref1.0 Ref
 NH-black9220.9 (0.9-1.0)4091.0 (0.9-1.1)1.0 (0.9-1.1)1.0 (0.9-1.2)
 NH-API6780.8 (0.7-0.9)3720.8 (0.7-1.0)0.8 (0.6-0.9)0.7 (0.6-1.0)
 Hispanic8360.8 (0.7-0.9)4810.8 (0.7-1.0)0.8 (0.7-1.0)0.8 (0.6-1.0)
 AI/AN491.5 (1.0-2.3)321.5 (0.8-2.5)1.9 (1.1-3.1)1.7 (1.0-3.2)
Health insurance      
 Employer/Medicare/private55951.0 Ref1.0 Ref
 Government781.5 (1.1-2.1)1.6 (1.1-2.3)
 Medicaid/not insured6941.4 (1.2-1.5)1.3 (1.1-1.4)
Years of education      
 <1236071.3 (1.2-1.4)16051.2 (1.1-1.4)1.4 (1.3-1.5)1.3 (1.1-1.4)
 1248141.2 (1.1-1.2)23061.1 (1.0-1.2)1.2 (1.1-1.3)1.2 (1.1-1.3)
 ≥1348101.0 Ref24561.0 Ref1.0 Ref1.0 Ref
Annual family income      
 <$10,00012881.3 (1.2-1.5)6461.3 (1.1-1.6)1.2 (1.1-1.4)1.2 (1.0-1.5)
 $10,000-$34,99949211.2 (1.1-1.3)24041.2 (1.0-1.3)1.1 (1.0-1.2)1.1 (1.0-1.3)
 ≥$35,00063141.0 Ref30241.0 Ref1.0 Ref1.0 Ref
 Unknown7111.1 (1.0-1.2)2930.2 (0.0-2.2)1.0 (0.9-1.2)0.3 (0.0-2.5)
Family poverty status, 1990 threshold      
 ≤100%10071.0 (0.9-1.2)4730.9 (0.7-1.1)1.0 (0.8-1.2)0.9 (0.7-1.1)
 100%-400%60901.0 (1.0-1.1)12481.0 (0.9-1.2)1.1 (1.0-1.2)1.1 (0.9-1.2)
 ≥400%59821.0 Ref17211.0 Ref1.0 Ref1.0 Ref
 Unknown1551.1 (1.0-1.2)29254.9 (0.5-43.7)1.0 (0.9-1.2)3.8 (0.4-34.5)
Surgery, cancer-directed      
 Yes72611.0 Ref34151.0 Ref1.0 Ref1.0 Ref
 No59732.2 (2.1-2.3)29522.4 (2.2-2.6)2.6 (2.4-2.8)2.8 (2.5-3.1)
Radiotherapy      
 Yes37611.0 Ref18541.0 Ref1.0 Ref1.0 Ref
 No94731.1 (1.0-1.1)45131.1 (1.0-1.2)1.0 (0.9-1.1)1.0 (0.9-1.1)

Compared with cases with employer, Medicare, or private health insurance, hazard ratios were significantly elevated among cases with either Medicaid or no health insurance. For example, among those with Medicaid or no insurance, after adjusting for socioeconomic attributes and first course therapy, the hazard ratio for all-cause mortality was 1.4 (95% CI, 1.2-1.5), and the hazard ratio for cancer-specific mortality was 1.3 (95% CI, 1.1-1.4). There was also a more favorable prognosis associated with higher SES based on education and income, but there was no change in risk of mortality associated with family poverty status (Table 5). Even in a further sensitivity analysis to break down those with 100% to 400% into <100%, 100% to <200%, and 200% to 400%, poverty status was not strongly associated with either all-cause or cancer specific mortality. Patients who did not receive cancer-directed surgery had less favorable outcome compared with those who did, whereas patients without radiotherapy experienced similar mortality to those receiving this therapy. There were no significant interactions between race/ethnicity and socioeconomic factors (including health insurance) on the risk of mortality.

Table 6 presents the racial/ethnic disparities in all-cause and cancer-specific mortality by tumor sites. For breast cancer, the hazard ratio for all-cause mortality was significantly higher among blacks compared with whites in models adjusted for patient and tumor characteristics (Model 1), socioeconomic factors (education and income/poverty) and treatment (Model 2), and after additional adjustment for health insurance (Model 3). There was no significant difference in breast cancer mortality among other ethnic groups. Among cases with colorectal cancer, blacks were significantly more likely than whites to die of any cause and of cancer-specific causes even after controlling for education, income, poverty, and treatment (Model 1 and Model 2), but the association was no longer significant after adjusting for health insurance (Model 3). Among men with prostate cancer, hazard ratio of cancer-specific mortality for blacks compared with whites was significantly higher even after controlling for socioeconomic factors, treatment, and health insurance. Among cases with urinary bladder cancer, hazard ratios of both all-cause and cancer-specific mortality were nearly twice as high among blacks, but were not significantly different from whites among other racial and ethnic groups after controlling for socioeconomic factors and treatment. Among cases with lung/bronchus, cervical, and ovarian cancer and melanoma, there were no significant differences in hazard ratios for blacks or any other racial or ethnic group compared with whites after fully adjusting for socioeconomic factors and treatment.

Table 6. Mortality in Association With Race/Ethnicity Among Patients With Invasive Tumors, by Tumor Site
Tumor SiteRace/ EthnicityHazard Ratio (95% CI) of All-Cause MortalityHazard Ratio (95% CI) of Cancer-Specific Mortality
Model 1Model 2Model 3Model 1Model 2Model 3
  1. CI indicates confidence interval; NH, non-Hispanic; API, Asian/Pacific Islander; AI/AN, American Indian/Alaska Native.

  2. NH whites as reference in all models. Model 1: Hazard ratio (HR) adjusted for age, sex, tumor stage, surgery, and radiotherapy. Model 2: HR additionally adjusted for education, poverty, and family income. Model 3: HR additionally adjusted for health insurance in subjects with data on health insurance.

BreastNH-black1.4 (1.2-1.8)1.2 (1.0-1.6)1.7 (1.1-2.5)1.2 (0.9-1.6)1.1 (0.8-1.5)1.4 (0.8-2.4)
NH-API0.6 (0.4-0.8)0.5 (0.4-0.9)0.6 (0.3-1.1)0.6 (0.3-1.0)0.6 (0.3-1.1)0.8 (0.4-1.7)
Hispanic1.0 (0.7-1.4)0.9 (0.7-1.2)1.1 (0.7-1.7)0.8 (0.5-1.3)0.7 (0.5-1.2)0.8 (0.4-1.5)
AI/AN0.1 (0.0-30.2)0.1 (0.0-29.3.3)Undefined0.1 (0.0-45.2)0.1 (0.0-55.5)Undefined
ColorectalNH-black1.4 (1.1-1.7)1.2 (1.0-1.5)1.2 (0.9-1.7)1.4 (1.1-1.8)1.2 (1.0-1.6)1.2 (0.8-1.8)
NH-API0.9 (0.7-1.1)0.9 (0.7-1.1)0.9 (0.6-1.3)0.8 (0.6-1.2)0.9 (0.6-1.2)0.9 (0.6-1.5)
Hispanic1.1 (0.8-1.4)1.0 (0.8-1.3)1.0 (0.7-1.5)1.1 (0.8-1.5)1.0 (0.7-1.3)1.1 (0.7-1.6)
AI/AN4.4 (1.8-10.9)4.8 (1.9-11.9)4.9 (1.9-12.7)6.1 (2.5-15.1)7.0 (2.8-17.4)6.6 (2.6-17.2)
ProstateNH-black1.2 (1.1-1.5)1.0 (0.9-1.2)1.1 (0.9-1.4)1.5 (1.2-1.8)1.3 (1.0-1.6)1.7 (1.2-2.3)
NH-API0.8 (0.6-1.1)0.8 (0.6-1.1)0.7 (0.5-1.2)0.5 (0.3-0.9)0.5 (0.3-0.9)0.4 (0.2-0.9)
Hispanic0.8 (0.6-1.1)0.7 (0.5-0.9)0.4 (0.3-0.8)0.9 (0.6-1.4)0.8 (0.5-1.2)0.4 (0.2-0.9)
AI/AN2.0 (0.7-5.3)1.8 (0.7-4.8)2.2 (0.7-6.9)1.6 (0.3-8.2)1.5 (0.3-7.4)1.7 (0.3-9.7)
Lung and bronchusNH-black1.1 (1.0-1.3)1.0 (0.9-1.2)1.1 (0.9-1.3)1.1 (1.0-1.3)1.1 (0.9-1.2)1.1 (0.9-1.3)
NH-API0.8 (0.7-1.0)0.8 (0.7-1.1)0.9 (0.6-1.2)0.8 (0.6-1.0)0.8 (0.6-1.0)0.8 (0.5-1.1)
Hispanic1.0 (0.8-1.2)0.9 (0.7-1.1)0.8 (0.6-1.1)1.0 (0.8-1.3)0.9 (0.7-1.2)0.8 (0.6-1.2)
AI/AN2.8 (1.3-5.8)2.1 (1.0-4.4)1.7 (0.7-4.3)3.1 (1.4-6.7)2.4 (1.1-5.2)2.0 (0.8-5.2)
CervicalNH-black0.6 (0.2-1.4)0.4 (0.2-1.2)0.1 (0.0-0.5)0.4 (0.2-1.3)0.4 (0.1-1.4)0.7 (0.1-5.8)
NH-API1.6 (0.6-4.3)1.6 (0.6-4.7)2.3 (0.3-19.7)2.3 (0.8-6.4)2.1 (0.7-6.8)3.5 (0.4-30.4)
Hispanic1.1 (0.5-2.3)1.0 (0.4-2.3)2.7 (0.6-12.6)1.3 (0.6-3.0)1.2 (0.4-3.0)1.4 (0.2-17.1)
AI/AN2.2 (0.2-21.3)1.1 (0.1-13.8)5.6 (0.0 to >99)2.4 (0.1-69.0)3.3 (0.1 to >99)408.7 (6.6 to >999)
OvarianNH-black1.2 (0.8-1.9)1.2 (0.8-1.9)1.5 (0.8- 3.0)1.1 (0.7-1.9)1.2 (0.7-2.0)1.3 (0.6-2.6)
NH-API0.3 (0.1-0.9)0.3 (0.1-1.0)0.2 (0.0-1.5)0.4 (0.1-1.1)0.4 (0.1-1.1)0.3 (0.0-1.7)
Hispanic0.9 (0.5-1.7)0.9 (0.5-1.6)1.3 (0.6-3.2)0.8 (0.4-1.5)0.7 (0.3-1.4)0.9 (0.3-2.7)
AI/AN1.4 (0.3-7.3)2.2 (0.4-12.5)Undefined1.6 (0.3-8.1)3.0 (0.5-17.5)Undefined
Melanoma of the skinNH-black1.7 (0.3-8.3)1.6 (0.3-8.2)Undefined3.6 (0.7-18.3)3.5 (0.7-18.4)Undefined
NH-API4.3 (1.5-11.9)4.7 (1.6-13.4)2.5 (0.6-11.1)4.9 (1.5-15.6)5.3 (1.6-17.3)0.8 (0.1-5.3)
Hispanic3.4 (1.2-9.9)4.2 (1.5-12.4)1.5 (0.3-7.7)4.5 (1.5-13.7)6.5 (2.2-19.6)1.5 (0.3-9.2)
AI/AN5.8 (0.6-59.0)3.5 (0.3-42.1)6.8 (0.4-103.4)UndefinedUndefinedUndefined
Urinary bladderNH-black1.5 (1.0-2.4)1.3 (0.8-2.0)2.0 (1.0-4.4)1.8 (1.0-3.1)1.7 (0.9-3.0)2.3 (0.9-6.0)
NH-API0.9 (0.5-1.5)0.9 (0.5-1.6)1.3 (0.6-2.7)0.9 (0.4-2.1)1.0 (0.4-2.2)1.2 (0.4-3.9)
Hispanic0.7 (0.3-1.5)0.6 (0.3-1.4)0.6 (0.2-1.8)0.7 (0.2-2.1)0.7 (0.2-2.1)0.7 (0.2-2.9)
AI/AN0.5 (0.1-1.8)0.7 (0.2-2.5)0.5 (0.1-2.6)0.3 (0.0-3.0)0.5 (0.1-4.7)Undefined

DISCUSSION

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONFLICT OF INTEREST DISCLOSURES
  7. REFERENCES

This study examined the effects of socioeconomic factors at the individual level (health insurance, education, income, and poverty status) and treatment on racial disparities in survival in large cohorts of cases that were diagnosed with the 8 most common types of cancer at age ≥25 years. Noteworthy findings included that even after controlling for socioeconomic factors and patient and tumor characteristics, blacks were significantly less likely to receive cancer-directed surgery compared with whites, possibly because of a less favorable stage distribution at diagnosis. Hazard ratios for all-cause and cancer-specific mortality for the 8 common tumors combined were no longer significantly higher among blacks after controlling for treatment and socioeconomic factors (education, income, and poverty), or after further adjusting for health insurance. However, substantially higher hazard ratios persisted for all-cause mortality among black women with breast cancer and for cancer-specific mortality among black men with prostate cancer compared with whites. These associations were not observed among other racial/ethnic groups. Future studies should assess the role of treatment and local area effects as well as individual level factors in minority disparities in cancer survival.

The differences in survival between black and white cases have been attributed to numerous factors.7-20 Although racial/ethnic differences were likely multifactorial, access to quality care and socioeconomic factors are prominent among these factors.10-24 Several studies demonstrated that if cases have equal access to quality healthcare, the outcomes are similar among different racial groups.10-13 Other studies showed that racial disparities still existed even after controlling for socioeconomic factors and for access to equitable care and treatment.10-13 These studies had variable quality data on SES, and the majority of studies relied on socioeconomic data at the area level (ie, zip code or census tract) rather than at the individual level. Our study included several socioeconomic variables at the individual level, including health insurance, years of education, family income, and poverty status. These unique data allow for a more complete adjustment for confounding by socioeconomic factors.

Differences in mortality between black and white cases were substantially reduced and were only marginally significant after adjusting for socioeconomic factors and treatment. This indicated that socioeconomic differences and treatment may play a major role in achieving equal outcomes for cases with cancer. These factors are generally modifiable. With improvement in these underlying factors, it may be more likely that national goals can be achieved,25 such as Healthy People 2010 and 2020 objectives to eliminate racial disparities in healthcare and outcomes.

Several limitations should be noted. Socioeconomic status (health insurance, education income, and poverty status) was obtained from participants at the time of survey rather than at the time of cancer diagnosis. It is possible that SES might have changed from the time of survey to the time of diagnosis, and therefore might not be the true SES that mattered most at the time of diagnosis, leading to a degree of exposure misclassification. However, because the study population was selected for subjects aged ≥25 years who were later diagnosed with cancer, they were less likely to change SES substantially, particularly regarding education level. The models used in this analysis did not adjust for area-level factors such as economic status and environmental or physical conditions, which could therefore contribute to residual confounding, because several studies indicated that neighborhood SES was an independent predictor of health outcomes,7, 8, 10-12 albeit often less influential than individual-level socioeconomic factors.7, 8 In addition, although information on cancer-directed surgery and radiation from SEER data was available, the lack of data on chemotherapy and hormone therapy was a limitation, as was the absence of data on occupational exposures that may contribute to urinary bladder cancer.

In summary, survival time from diagnosis was significantly decreased among cancer cases with low compared with those with high SES. Hazard ratios for all-cause and cancer-specific mortality among blacks compared with whites for 8 leading tumors combined lost statistical significance after adjusting for socioeconomic factors and treatment. Blacks had unfavorable prognoses compared with whites even after adjustment for SES and treatment for several leading tumor sites such as breast, colorectal, and urinary bladder cancer, as did hazard ratios for disease-specific survival after diagnosis of colorectal and prostate cancer. Future population-based studies examining racial/ethnic disparities in cancer care and outcomes should include detailed measures of all treatment modalities rendered and account for both individual level and area socioeconomic factors.

CONFLICT OF INTEREST DISCLOSURES

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONFLICT OF INTEREST DISCLOSURES
  7. REFERENCES

We acknowledge contributions to the National Longitudinal Mortality Study by the US Bureau of the Census, the National Cancer Institute, and SEER tumor registries in creating this database. Data analysis was supported by Interagency Agreement Y1-PC-9021 between the National Cancer Institute and the Census Bureau. We thank Loreta Ajagba for preparing the tables presented in this report.

REFERENCES

  1. Top of page
  2. Abstract
  3. MATERIALS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. CONFLICT OF INTEREST DISCLOSURES
  7. REFERENCES