The expanding melanoma burden in California hispanics

Importance of socioeconomic distribution, histologic subtype, and anatomic location

Authors

  • Ricardo A. Pollitt MD, PhD,

    Corresponding author
    1. Department of Dermatology, Pigmented Lesion and Melanoma Program, Stanford University Medical Center and Stanford Cancer Center, Stanford, California
    • Department of Dermatology, Stanford University Medical Center, 450 Broadway Street, Pavilion C, Second Floor, Redwood City, CA 94063
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    • Fax: (650) 721-3464

  • Christina A. Clarke PhD, MPH,

    1. Northern California Cancer Center, Fremont, California
    2. Department of Health Research and Policy, Stanford University Medical Center and Stanford Cancer Center, Stanford, California
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  • Susan M. Swetter MD,

    1. Department of Dermatology, Pigmented Lesion and Melanoma Program, Stanford University Medical Center and Stanford Cancer Center, Stanford, California
    2. Dermatology Service, Veterans Affairs Palo Alto Health Care System, Palo Alto, California
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  • David H. Peng MD, MPH,

    1. Department of Clinical Dermatology, University of Southern California, Los Angeles, California
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  • John Zadnick MS,

    1. Department of Preventive Medicine, University of Southern California/Keck School of Medicine, Los Angeles, California
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  • Myles Cockburn PhD

    1. Department of Preventive Medicine, University of Southern California/Keck School of Medicine, Los Angeles, California
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  • The ideas and opinions expressed herein are those of the authors, and endorsement by the State of California Department of Public Health, the National Cancer Institute, the Centers for Disease Control and Prevention, or their contractors and subcontractors is not intended nor should be inferred.

Abstract

BACKGROUND:

The incidence patterns and socioeconomic distribution of cutaneous melanoma among Hispanics are poorly understood.

METHODS:

The authors obtained population-based incidence data for all Hispanic and non-Hispanic white (NHW) patients who were diagnosed with invasive cutaneous melanoma from 1988 to 2007 in California. By using a neighborhood-level measure of socioeconomic status (SES), the variables investigated included incidence, thickness at diagnosis, histologic subtype, anatomic site, and the relative risk (RR) for thicker (>2 mm) versus thinner (≤2 mm) tumors at diagnosis for groups categorized by SES.

RESULTS:

Age-adjusted melanoma incidence rates per million were higher in NHWs (P < .0001), and tumor thickness at diagnosis was greater in Hispanics (P < .0001). Sixty-one percent of melanomas in NHWs occurred in the High SES group. Among Hispanics, only 35% occurred in the High SES group; and 22% occurred in the Low SES group. Lower SES was associated with thicker tumors (P < .0001); this association was stronger in Hispanics. The RR of thicker tumors versus thinner tumors (≤2 mm) in the Low SES group versus the High SES group was 1.48 (95% confidence interval [CI], 1.37-1.61) for NHW men and 2.18 (95% CI, 1.73-2.74) for Hispanic men. Patients with lower SES had less of the superficial spreading melanoma subtype (especially among Hispanic men) and more of the nodular melanoma subtype. Leg/hip melanomas were associated with higher SES in NHW men but with lower SES in Hispanic men.

CONCLUSIONS:

The socioeconomic distribution of melanoma incidence and tumor thickness differed substantially between Hispanic and NHW Californians, particularly among men. Melanoma prevention efforts targeted to lower SES Hispanics and increased physician awareness of melanoma patterns among Hispanics are needed. Cancer 2011. © 2010 American Cancer Society.

Melanoma incidence has increased substantially worldwide over the last few decades,1-5 and melanoma has become a leading cause of cancer deaths in young adults.6-8 Most previous studies examining the expanding burden of melanoma in the United States focused on non-Hispanic white (NHW) populations in whom incidence is highest.9 However, little is known about the burden of melanoma among Hispanics, who comprise approximately 15% of the US population and represent its fastest growing ethnic group. In California, >36% of the population is Hispanic.10 Melanoma incidence rates in the United States are lower among Hispanics (4.5 per 100,000) than among NHWs (21.6 per 100,000),8 but melanomas in Hispanics are thicker and of later stage at diagnosis, are more likely to metastasize, and have worse overall outcomes than melanomas in NHWs.7, 11-17 Clinical characteristics, including anatomic site of presentation and histologic subtype, also differ between Hispanics and NHWs, with more melanomas on the legs11, 14, 15, 18 and a greater frequency of the acral lentiginous subtype (which occur on the palms, soles, and subungual areas) reported in Hispanics.12, 14, 15 Among California Hispanics, increasing melanoma incidence from 1988 to 2001 was confined to thicker (>1.5 mm) tumors (associated with a worse prognosis),19, 20 a trend that was not observed among NHWs.21 A recent Florida study reported that the proportion of melanomas diagnosed at a late stage among Hispanics improved little from 1990 to 2004 compared with the significant improvements observed among NHWs.17

The later stage at diagnosis and worse prognosis in Hispanics have been attributed to several factors, including lower access to health insurance,22 delays in seeking treatment,15, 23 less awareness of risks or symptoms,15, 24 a lack of linguistically or culturally targeted screening efforts,25 and declines in sun-safe behaviors because of increasing acculturation.26 Many of these factors may be associated with lower socioeconomic status (SES). Previous studies reported higher rates of melanoma in high SES populations but greater prevalence of late-stage melanoma and worse outcomes among low SES, uninsured, or poorly insured populations.14, 16, 27-31 Therefore, SES may represent a critical component in understanding the melanoma burden among Hispanics, because Hispanics are more concentrated in lower SES communities than NHWs.

To further understand the burden of melanoma in Hispanics and especially how SES influences this burden, we focused on the large Hispanic population of California and examined differences in melanoma characteristics between all Hispanics and NHWs who were diagnosed with cutaneous malignant melanoma in California from 1988 to 2007. Our primary objective was to describe racial/ethnic differences in the socioeconomic distribution of overall melanoma incidence and the incidence of thicker (>2 mm) tumors. We also examined differences in the socioeconomic distribution of melanoma histologic subtype and anatomic location.

MATERIALS AND METHODS

Source of Cancer Cases

Population-based melanoma incidence data were obtained from the California Cancer Registry (CCR), the statewide population-based cancer registry (www.ccrcal.org accessed June 2009) that contributes data to the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) Program. Patients were residents of California who were diagnosed with invasive cutaneous melanoma (International Classification of Diseases, third edition [ICD-O-3] histology codes 8720-8790) between January 1, 1988 and December 31, 2007.

Patient Demographic and Tumor Characteristics

Patient race/ethnicity was categorized as either NHW or Hispanic based on medical record reports of race/ethnicity supplemented by use of the National Hispanic Identification Algorithm.11 Patient SES was assigned on the basis of residence at diagnosis. We used an index SES measure that incorporated US Census information on census block group-level education, median household income, proportion living 200% below poverty level, proportion of blue-collar workers, proportion aged >16 years and unemployed, median rent, and median house value. This index was developed using principal components analysis as described by Yost et al32 and was used previously.5, 32, 33 Patients with unknown block group of residence (8.7%) were assigned randomly to a block group within their county. Standardized component scores for the index were categorized into quintiles (quintile 1 was lowest SES, and quintile 5 was highest SES).

Given the limited number of Hispanics of higher SES, the 2 highest SES quintiles were grouped into a High SES group, and the third and fourth quintiles were grouped into a Middle SES group. The 3 SES groups (High, Middle, and Low) were used in SES-specific analyses.

Melanoma tumor thickness (≤1.00 mm, 1.01-2.00 mm, 2.01-4.00 mm, and ≥4.01 mm) was classified according to 2002 American Joint Committee on Cancer tumor categories.34 Histologic subtype was classified by ICD-O-3 code as superficial spreading melanoma (SSM) (code 8743), nodular melanoma (NM) (code 8721), acral lentiginous melanoma (ALM) (code 8744), and lentigo maligna melanoma (code 8742). Specified rare histologies (codes 8722-8741 and 8745-8790) were grouped with malignant melanomas of unspecified histology (MM/NOS) (code 8720), and 99.97% of cases were confirmed microscopically. Anatomic site was categorized as head/neck (codes C44.0-C44.4), upper limb/shoulders (code C44.6), trunk (code C44.5), and lower limbs/hips (code C44.7).

Statistical Analysis

SEER*Stat software (SEER Program, National Cancer Institute, Bethesda, Md) was used to calculate case distributions and annual age-adjusted incidence rates (AAIRs) per 1,000,000 population (standardized to the 2000 US standard population) with 95% confidence intervals (CIs) for cutaneous melanoma from 1988 to 2007. Distributions were compared using chi-square and Fisher exact tests (specific tests are noted in table footnotes). We estimated the relative risk (RR) for case count data using the logit odds ratio. We calculated tests of linear trend using the Cochran-Armitage test for linearity. P values <.05 were considered statistically significant.

The SES distribution of the Hispanic and NHW populations varied by age, and there was a higher proportion of High SES Hispanics in younger age groups. Our SES measure was at the census block-group level, and population denominators at this level are available from the US Bureau of the Census only for decennial census years (1990 and 2000). Therefore, SES-specific AAIRs could be calculated only for the years 1988 through 2002 (for which census-based denominators are likely to be stable) according to our previous approach.5 We calculated AAIRs restricted to 1998 through 2002 in separate analyses (data not shown). We observed no substantial differences between the results from those age-adjusted rate analyses and the results presented below.

RESULTS

Table 1 provides sociodemographic and clinical data for 83,859 NHW and 4607 Hispanic Californians with incident melanomas reported between 1988 and 2007. The median age at diagnosis was significantly higher among NHWs (men, 61 years; women, 54 years) than among Hispanics (men, 55 years; women, 47 years; P < .0001). Hispanics had significantly lower neighborhood-level SES: >40% of Hispanic patients with melanoma were in quintile 1 (the lowest) or quintile 2 of neighborhood SES versus 20% of NHWs, whereas only 16% of Hispanics were in quintile 5 (the highest) of neighborhood SES compared with 33% to 35% of NHWs (P < .0001 for all).

Table 1. . Melanoma Incidence in Hispanics and Non-Hispanic Whites in California by Age, Socioeconomic Status, and Melanoma Tumor Characteristics: 1988-2007 (N=88,466)
VariableNo. of Patients (%)
MenWomen
NHWHispanicNHWHispanic
  • NHW indicates non-Hispanic white; SES, socioeconomic status; SSM, superficial spreading melanoma; NM, nodular melanoma; ALM, acral lentiginous melanoma; LMM, lentigo maligna melanoma.

  • a

    P values from chi-square test comparing NHWs and Hispanics across all nonmissing categories.

  • b

    SES quintiles were calculated using a composite SES index incorporating US Census block group-level data on education, median household income, proportion living 200% below the Federal Poverty Level, proportion of blue-collar workers, proportion aged >16 years and unemployed, and median rent and house value. Based on data from principal component analysis as described by Yost K, Perkins C, Cohen R, Morris C, Wright W. Socioeconomic status and breast cancer incidence in California for different race/ethnic groups. Cancer Causes Control. 2001;12:703-711.32

Age, y
 0-4913,386 (27.3)740 (38.4)14,302 (41.1)1471 (54.6)
 50-6414,481 (29.5)516 (25.6)8768 (25.2)590 (21.9)
 ≥6521,152 (43.2)656 (36)11,770 (33.7)634 (23.5)
 P <.0001a <.0001a
SES quintile2b
 5, Highest17,204 (35.1)306 (16)11,489 (33)445 (16.5)
 412,721 (26)322 (16.8)9336 (26.8)543 (20.2)
 39548 (19.5)385 (20.1)7110 (20.4)585 (21.7)
 26500 (13.3)432 (22.6)4736 (13.6)571 (21.2)
 1, Lowest3046 (6.2)467 (24.4)2169 (6.2)551 (20.5)
 P <.0001 <.0001
Thickness, mm
 ≤125,454 (51.9)712 (37.2)20,501 (58.8)1360 (50.5)
 1.01-26958 (14.2)278 (14.5)4503 (12.9)374 (13.9)
 2.01-44219 (8.6)223 (11.7)2286 (6.6)236 (8.8)
 ≥4.012538 (5.2)186 (9.7)1220 (3.5)163 (6.1)
 Unknown9850 (20.1)846 (26.8)6330 (18.2)562 (20.9)
 P <.0001 <.0001
Histology
 SSM14,131 (28.8)417 (21.8)11,730 (33.7)839 (31.1)
 NM4126 (8.4)233 (12.2)2393 (6.9)221 (8.2)
 ALM290 (0.6)113 (5.9)306 (0.9)109 (4)
 LMM2935 (6)71 (3.7)1471 (4.2)60 (2.2)
 Rare histologic subtypes3139 (6.4)115 (6)1747 (5)125 (4.6)
 P <.0001 <.0001
 Unspecified24,398 (49.8)963 (50.4)17,193 (49.5)1341 (49.8)
Anatomic site
 Head/neck12,069 (26.2)419 (24.4)4854 (14.5)399 (15.7)
 Trunk18,947 (41.1)562 (32.7)8388 (25.1)601 (23.7)
 Upper limbs/shoulders10,873 (23.6)308 (17.9)9497 (28.5)649 (25.6)
 Lower limbs/hip4234 (9.2)430 (25)10,648 (31.9)891 (35.1)
 P <.0001 .0003

Among men, the average annual age-adjusted incidence rate was 286.1 per 1,000,000 for NHWs and 41.3 per 1,000,000 for Hispanics (P < .001). Among women, the rate was 183.7 per 1,000,000 NHWs and 41.8 per 1,000,000 Hispanics (P < .001). Sex-specific rates varied by race/ethnicity: Men accounted for 58% of melanomas among NHWs but only 42% of melanomas among Hispanics (P < .0001).

Clinical Melanoma Characteristics

Tumor thickness data were missing for 31% of NHW patients and for 35% of Hispanic patients, consistent with other data from population-based cancer registries. There was a significant association between missing/unknown tumor depth and SES among both Hispanics and NHWs (P < .0001; data not shown). However, this association did not vary substantially by race/ethnicity: 30% of NHWs were missing information on tumor depth in quintile 1 (lowest SES quintile), and 19% were missing this information in quintile 5 (highest SES quintile); whereas 33% and 21% of Hispanics were missing information on tumor depth in quintiles 1 and 5, respectively.

Missing information on tumor thickness was strongly associated with disease stage: For regional/distant (vs localized) disease stage, NHWs had a steadily increasing socioeconomic gradient of missing data (9% in quintile 5 increasing to 15% in quintile 1; data not shown). Among Hispanics, these rates of missing data increased similarly from 12.5% in quintile 5 up to 25% in quintile 1.

Among those with known tumor thickness, distributions differed significantly by race/ethnicity and sex. The mean age-adjusted tumor thickness was greater among Hispanic men (1.80 mm) versus NHW men (1.22 mm; P < .0001) and among Hispanic women (1.47 mm) versus NHW women (1.07 mm; P < .0001). In addition, a significantly higher percentage of Hispanic men versus NHW men had tumors >2 mm thick at diagnosis (21% vs 14%, respectively; P < .0001). This difference also was observed for the thickest tumors (>4 mm): Approximately twice as many Hispanic men (10%) as NHW men (5%) had tumors >4 mm thick. An excess of thicker tumors also was observed among Hispanic women (15% had tumors >2 mm thick) compared with NHW women (10%).

The ALM and NM subtypes comprised a greater percentage of melanomas among Hispanic men than among NHW men (Table 1) (P < .001), whereas the SSM subtype comprised a smaller percentage (P < .0001). Aside from ALM, the distribution of histologic subtypes of melanoma was similar in Hispanic women and NHW women. In both racial/ethnic groups, the frequency of MM/NOS histology increased with decreasing SES: MM/NOS frequency increased from 46% in quintile 5 (highest SES quintile) to 51% in quintile 1 among NHWs and from 46% in quintile 5 to 53% in quintile 1 among Hispanics (data not shown). Hispanic men had a significantly higher incidence of tumors on the lower limbs/hips than NHW men (25% vs 9%; P < .001) and a lower incidence of tumors on the trunk (33% vs 41%; P < .0001).

Socioeconomic Status and Percentage of Thicker (>2 mm) Melanomas at Diagnosis

Patients with lower SES were more likely to have thicker tumors at diagnosis irrespective of race/ethnicity or sex (P for trend <.0001 for all) (Table 2). The association between lower SES and thicker tumors was considerably stronger among Hispanic men than among NHW men. Compared with NHW men in the High SES group, the relative risk (RR) for having tumors >2 mm among NHW men in the Middle SES and Low SES groups men was 1.26 (95% CI, 1.20-1.32) and 1.48 (95% CI, 1.37-1.61), respectively. Compared with Hispanic men in the High SES group, the RR for thicker tumors was 1.77 (95% CI, 1.42-2.20) for Hispanic men in the Middle SES group and 2.18 (95% CI, 1.73-2.74) for Hispanic men in the Low SES group. These findings also held true for women: NHW women in the Low SES group had an RR of 1.63 (95% CI, 1.46-1.83) for thicker tumors compared with NHW women in the High SES group, whereas the RR increased to 1.98 (95% CI, 1.55-2.51) in Hispanic women in the Low SES group compared with the High SES group.

Table 2. Melanoma Occurrence by Tumor Thickness at Diagnosis and Relative Risk of Thicker (>2 mm) Versus Thinner (≤2 mm) Melanoma According to Socioeconomic Status Stratified by Race/Ethnicity and Sex: California, 1988-2007 (N=88,466)
Tumor Thickness, mmHigh SESMiddle SESLow SESP for Trendb
No. (%)RRaNo. (%)RR [95% CI]aNo. (%)RR [95% CI]a
  • SES indicates socioeconomic status; RR< relative risk; CI, confidence interval; NH non-Hispanic.

  • a

    The RR is the logit estimate of the odds ratio (and 95% CI) comparing the risk of having thick melanoma (>2 mm) versus thin melanoma (≤2 mm) at diagnosis for patients in each group versus patients in the high SES group of the same sex and race/ethnicity group.

  • b

    Cochran-Armitage test for linearity; P values indicate no linear trend in the proportion of thick tumors across SES groups.

Men
 NH white
  ≤220,775 9946 1691  
  >23832 (16)1.002418 (20)1.26 [1.20-1.32]507 (23)1.48 [1.37-1.61]<.0001
 Hispanic
  ≤2399 407 184  
  >290 (18)1.00196 (33)1.77 [1.42-2.20]123 (40)2.18 [1.73-2.74]<.0001
Women
 NH white
  ≤215,515 8144 1345  
  >21882 (11)1.001336 (14)1.30 [1.22-1.39]288 (18)1.63 [1.46-1.83]<.0001
 Hispanic
  ≤2693 740 301  
  >2106 (13)1.00186 (20)1.51 [1.22-1.88]107 (26)1.98 ]1.55-2.51]<.0001

Greater than 60% of NHWs with melanoma were in the High SES group. Among Hispanics, however, individuals in the High SES group comprised only 33% of those with melanoma (P < .0001). Conversely, NHWs in the Low SES group included only 6% of all NHW patients with melanoma, whereas >20% of Hispanic patients with melanoma were in the Low SES group (P < .0001).

This racial/ethnic difference in tumor burden by SES was stronger among those with thicker tumors (>2 mm). Among NHWs, >50% of these tumors occurred in the High SES group; whereas, among Hispanic men and women, only 19% and 24% of thicker tumors, respectively, occurred in the High SES group (P < .0001 for both sexes). Conversely, only 8% of thicker tumors occurred among NHWs in the Low SES group, whereas 30% and 26% of thicker tumors occurred among Hispanic men and women, respectively, in the Low SES group (P < .0001 for both sexes).

Socioeconomic Status and Melanoma Histologic Subtype

Among men, patients with lower SES had a lower percentage of the SSM subtype (P for trend <.0001 within both races/ethnicities) (Table 3). Again, this association was stronger in Hispanic men than in NHW men. An association between lower SES and a higher percentage of patients with the NM subtype was observed in all groups; there was little difference in the strength of this association by race/ethnicity or sex (P for trend: NHW men, P < .0001; Hispanic men, P = .0004; NHW women, P < .0001; and Hispanic women, and P = .039) (Table 3).

Table 3. Histologic Melanoma Subtype by Socioeconomic Status Group in Hispanic and Non-Hispanic White Men and Women: California, 1988-2007 (N=88,466)
Histologic Subtype of MelanomaHigh SESMiddle SESLow SESP for Trendb
No.%PaNo.%PaNo.%Pa
  • SES indicates socioeconomic status; NHW, non-Hispanic white; SSM, superficial spreading melanoma; NM, nodular melanoma; NOS, not otherwise specified.

  • a

    Chi-square P value for the difference between the percentage of Hispanic patients and NHW patients with a specific melanoma subtype within a specific SES group by sex.

  • b

    Cochran-Armitage P value for statistical significance of a linear trend in the frequency of a specific melanoma subtype by SES within racial/ethnic and sex subgroups.

Men
 NHW
  SSM904630.2 431926.9 76625.2 <.0001
  NM22977.7 14909.3 33911.1 <.0001
  Other/unknown18,58262.1 10,23963.8 194163.7  
 Hispanic
  SSM17828.3.2916920.7<.00017015<.0001<.0001
  NM518.1.6912214.9<.00016012.9.18.0004
  Other/unknown39963.5.4352664.4.4133772.2.002 
Women
 NHW
  SSM731235.1 378732 63129.1 <.0001
  NM12245.9 9478 22210.2 <.0001
  Other/unknown12,28959 711260 131660.7  
 Hispanic
  SSM34234.6.5934329.7.08315428.7<.0001
  NM676.8.27978.4.675710.3.87.039
  Other/unknown57958.6.9971661.9.1634061.7.80 

Socioeconomic Status by Anatomic Site of Melanoma

NHW men in the High SES group had more lower limb/hip melanomas than NHW men in the Low SES group (10% vs 7%; P < .0001) (Table 4). Conversely, Hispanic men in the High SES group had significantly lower proportions of these melanomas than Hispanic men in the Low SES group (19% vs 27%; P for trend = .0002). Although the percentage of melanomas on the trunk was stable across SES categories for NHW men, it was significantly higher among High SES versus Low SES Hispanic men (34% vs 23%; P for trend = .0003). Head/neck and upper limb and shoulder melanoma rates did not vary by SES among NHW men or Hispanic men.

Table 4. Anatomic Site of Melanoma by Socioeconomic Status Group in Hispanic and Non-Hispanic White Men and Women: California, 1988-2007 (N=88,466)
Anatomic Site of MelanomaHigh SESMiddle SESLow SESP for Trendb
No.%PaNo.%PaNo.%Pa
  • SES indicates socioeconomic status; NHW, non-Hispanic white; NOS, not otherwise specified.

  • a

    Chi-square P value for the difference between the percentage of Hispanic patients and NHW patients with a specific anatomic location of melanoma within a specific SES group by sex.

  • b

    Cochran-Armitage P value for statistical significance of a linear trend in the frequency of a specific anatomic location of melanoma by SES within racial/ethnic and sex subgroups.

Men
 NHW
  Upper limb and shoulder673522.5 347321.6 66521.8 .48
  Head/neck718124 411925.7 76925.3 <.0001
  Trunk11,60138.8 621638.7 113037.1 .55
  Lower limb and hip28429.5% 11817.4 2116.9 <.0001
  Overlap/NOS15665.2 10596.6 2718.9  
 Hispanic
  Upper limb and shoulder10516.7.00213316.3<.00017015.004.74
  Head/neck13421.3.2718722.9<.00019821<.001.64
  Trunk21634.4.1123929.3<.000110722.9<.0001.0003
  Lower limb and hip12019.1<.000118322.4<.000112727.2<.0001.0002
  Overlap/NOS538.4 759.2 6513.9  
Women
 NHW
  Upper limb and shoulder560126.9 327927.7 61728.5 .005
  Head/neck268412.9 180115.2 36917 <.0001
  Trunk508524.4 284524 45821.1 .036
  Lower limb and hip670232.2 333228.1 61428.3 .001
  Overlap/NOS7533.6 5895 1115.1  
 Hispanic
  Upper limb and shoulder26326.6.7026122.6<.000112522.7.009.034
  Head/neck12512.7.8816514.3<.000110919.8<.0001.0004
  Trunk22823.1.6727623.9<.00019717.6<.0001.027
  Lower limb and hip30731.1.9439834.4<.000118633.8<.0001.23
  Overlap/NOS656.6 564.8 346.2  

Associations between SES and anatomic location of melanomas did not vary as greatly by race/ethnicity among women. Among both NHW women and Hispanic women, head/neck melanomas were significantly more common in the Low SES groups. Unlike in men, lower limb and hip melanomas were only slightly more common among Hispanic women in the Low SES group versus the High SES group.

DISCUSSION

In this study, the largest analysis of melanoma incidence in US Hispanics to date, we observed that the distribution and overall burden of cutaneous melanoma, and particularly the associations between SES and melanoma incidence and thickness, differed substantially between Hispanic Californians and NHW Californians. Consistent with previous studies, our results revealed that Hispanics had a lower incidence of melanoma than NHWs but also were more likely to have thicker tumors at diagnosis.7, 35-37 In addition, however, we observed a much stronger burden of disease among lower SES Hispanics than among NHWs, particularly for men. The association between low SES and higher risk of thicker tumors at diagnosis was also much stronger among Hispanic men. In secondary analyses, we observed that SES was strongly associated with anatomic site of melanoma in Hispanic men (unlike in NHW men), making clinicians' experience with melanoma in NHW patients potentially less applicable among Hispanics. In addition, unlike in NHWs, melanoma histologic subtype differed strongly by SES among Hispanic men, with less SSM and more NM (the subtype accounting for most thicker melanomas)38 in lower SES Hispanic men.

Because this was the first large, population-based study with adequate numbers of patients to examine socioeconomic differences between Hispanic and NHW melanoma patients, we observed that roughly 66% the melanoma burden among Hispanic men occurred among those in the Middle SES and Low SES groups. By contrast, >60% of melanomas among NHWs occurred among those in the High SES group. These findings underscore the very different sociodemographic distribution of malignant melanoma in Hispanic versus NHWs Californians. Clearly, for California Hispanics, melanoma is not a “disease of the affluent” as it has been described among NHWs.35

The association between lower SES and thicker melanoma also was stronger among Hispanics: Melanomas among Hispanics in the Low SES group were more than twice as likely to be >2 mm thick than melanomas among Hispanics in the High SES group. Our results suggest that Hispanics of lower SES may have poorer access to social, cultural, educational or job-related benefits, which increases the physician delay in melanoma diagnosis compared with their lower SES NHW counterparts. Differences between lower SES and higher SES Hispanics are likely to be complex and may involve language barriers, knowledge about and access to health institutions, and/or other difficult-to-measure components of social capital.39, 40 Sun-related behaviors and cultural norms also may differentially impact melanoma risk and detection among Hispanics of lower SES.26, 41

We previously confirmed the reported higher frequency of the NM subtype and lower frequency of the SSM subtype among Hispanics compared with NHWs.11, 15, 42 The socioeconomic gradients observed in the distribution of melanoma subtypes were stronger for Hispanics. The frequency of the SSM subtype in particular decreased sharply in Hispanic men of lower SES, whereas the frequency of NM was higher. The reasons for these findings are unclear but may reflect racial/ethnic genetic susceptibilities for the development of various melanoma subtypes or environmental differences in the effect of chronic versus intermittent ultraviolet exposure on melanoma location and subtype. These novel findings require confirmation and further investigation.

We also confirmed previous reports that Hispanics have more leg/hip melanomas and less truncal melanomas than NHWs.11, 15, 43 Leg/hip melanomas include those on the soles; therefore, significantly higher rates of ALM among Hispanics help explain these findings.42 Racial/ethnic differences in distribution according to anatomic site were much stronger among men than women, however, which cannot be explained by the increased rates of ALM among Hispanics. More detailed analyses will be required to elucidate associations between anatomic site and histopathology of melanoma by race/ethnicity.

Leg/hip melanomas were much more common among Hispanic men of low SES versus high SES, whereas these melanomas actually were less common in low SES versus high SES NHW men. Conversely, the frequency of melanomas on the trunk was lower among Hispanic men of lower SES, but it did not vary appreciably by SES among NHWs. These SES associations suggest that the causes of racial/ethnic differences in anatomic distribution of melanoma are not purely biologic. Although Hispanics of lower SES may be more likely to work in outdoor occupations in which their lower limbs receive greater sun exposure, previous studies have not revealed an association between continuous occupational sun exposure and increased melanoma incidence.44 The role of ultraviolet exposure in melanoma incidence among Hispanics remains poorly defined with conflicting findings in previous studies.45, 46 Regardless, our data do suggest that dermatologists and primary care physicians should be aware of the importance of examining the skin on the hips and lower extremities of Hispanic men.

For the current analysis, we used a large, reliable, and up-to-date data source in the CCR, with access to all reported melanoma cases during the period analyzed in the US state with the largest population of Hispanics. In addition, our SES measure was created using a previously established measure that has been used in multiple published studies. However, our study also has several important limitations. First, our SES measure was an area-level measure and not an individual-level measure. Thus, observed SES differentials may relate to individual-level or a mixture of individual-level and neighborhood-level influences. The mean individual-level SES of Hispanics and NHWs living in the same SES-categorized neighborhood also may be different. The CCR data are limited further in that they do not provide information on health insurance status or on certain melanoma anatomic sites, such as plantar or subungual melanoma. Similarly, anatomic site-coding schemes in the CCR and in other existing population-based registries do not differentiate melanomas on the legs from those on the hips (an area that receives less sun exposure).

Missing data rates were moderately high: Thirty-one percent of NHWs and 35% of Hispanics were missing information on tumor thickness, but this was consistent with other population-based cancer registries. Missing thickness and histology also was associated inversely with SES; however, the associations were of similar magnitude in NHWs and Hispanics, so variations in missing data are unlikely to explain the observed differences between them. Histologic subtype was unspecified in approximately 50% of patients (although 99.97% of melanoma NOS cases were confirmed microscopically). Finally, it is important not to over generalize typical melanoma characteristics or presentation in a given population.

Altogether, our data suggest the need for different approaches to melanoma prevention and management in Hispanic populations than in NHW populations. Racial/ethnic differences in the socioeconomic distribution, socioeconomic gradient, thickness at diagnosis, and anatomic location of melanoma suggest that the screening approaches used for NHWs may not effectively target Hispanics. Cockburn et al21 demonstrated that the incidence rate of thicker (>1.5 mm) melanomas was increasing in California Hispanics and recommended primary and secondary prevention messages targeted to Hispanics. The lower SES of Hispanic melanoma patients and the clear SES gradient in tumor thickness underline the need for these prevention messages to be accessible to those who 1) have a limited education, 2) have limited English language skills or speak only Spanish, 3) have recently immigrated to the United States, or 4) have limited knowledge of and access to the American healthcare system. Such messages should include information regarding sun avoidance and protection as well as melanoma detection and skin self-examination techniques.

Clinicians also should take note of the marked racial/ethnic and socioeconomic differences in histologic subtype, anatomic location, and tumor thickness that were observed in the current study. In particular, health providers should be aware of the greater likelihood of thicker melanomas and more frequent tumors on the legs/hips in Hispanic men of lower SES.

Our observations of substantially greater proportions of thick melanomas among Hispanic men of lower SES men in California serve as a public health warning regarding the need for effective management of melanoma in minority and poorer populations. Although the absolute risk for melanoma is much lower among Hispanics, the large racial/ethnic disparities and socioeconomic gradients reported here indicate that melanoma prevention efforts in this population remain inadequate. Many fatal melanomas could be prevented every year by concerted efforts to improve 1) prevention messages directed specifically at Hispanics and 2) awareness among healthcare practitioners of the risk for cutaneous melanoma among Hispanics in the United States.

CONFLICT OF INTEREST DISCLOSURES

This work was supported by the National Cancer Institute's SEER Program under contract N01-PC-35136 awarded to the Northern California Cancer Center and contract N01-PC-35139 awarded to the University of Southern California. The collection of cancer incidence data used in this study was supported by the California Department of Public Health as part of the statewide cancer reporting program mandated by California Health and Safety Code Section 103885; the National Cancer Institute's SEER Program under contract N01-PC-35136 awarded to the Northern California Cancer Center, contract N01-PC-35139 awarded to the University of Southern California, and contract N01-PC-54404 awarded to the Public Health Institute; and the Centers for Disease Control and Prevention's National Program of Cancer Registries, under agreement 1U58DP00807-01 awarded to the Public Health Institute. Myles Cockburn was supported in part by National Institute of Environmental Health Sciences grant 5P30 ES07048 and National Institutes of Health grants R01 CA121052 and R01 ES015552.

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