United States Hispanics have seven times lower melanoma incidence rates than non-Hispanic whites (NHW). It is unclear whether this difference can be explained solely by phenotypic risk factors, like darker skin, or whether modifiable risk factors, like sun exposure, also play a role. The purpose of this paper is to summarize what is currently known about melanoma risk factors among Hispanics and NHWs, and whether or not those differences could explain the difference in melanoma incidence. Through literature review, relative risks and prevalence of melanoma risk factors in Hispanics and NHWs were identified and used to calculate the expected rate in Hispanics and rate ratio compared to NHWs. We found that melanoma risk factors either have similar frequency in Hispanics and NHWs (e.g., many large nevi) or are less frequent in Hispanics but do not explain a high proportion of disease variation (e.g., red hair). Considering current knowledge of risk factor prevalence, we found that melanoma incidence rates in the two groups should actually be similar. Sun exposure behavior among Hispanics may contribute to the explanation for the 7-fold difference in melanoma rates. Currently, limited data exist on sun exposure behavior among Hispanics, but possibilities for improving primary prevention by further studying these practices are substantial.
Hispanics are the largest ethnic group in the United States, and over the last few decades, rates of melanoma among Hispanics have steadily risen [
In this review, we examined what is currently known about the risk factors for melanoma and their distribution among Hispanics and then calculated expected rate ratios (NHW compared to Hispanic) for each risk factor based on published estimates of relative risk and risk factor prevalence in the two groups. We found that, based on what is currently known about the risk factors, the rates of melanoma among Hispanics and NHWs should be quite similar, and the fact that they are not similar may present an opportunity to investigate modifiable risk factors for melanoma—for which very little data exists in the Hispanic population—and to improve prevention efforts.
For summary relative risk (RR) measures for melanoma risk factors, we used a comprehensive meta-analysis by Gandini et al. of 83 observational studies through September 2002 [
Phenotypic risk factors for melanoma in the meta-analysis include blonde or red hair, many freckles, nevus counts, and Fitzpatrick phototype I or II. For freckles, the RR presented in the meta-analysis compared estimates for high versus low density of freckles. We focus on risk associated with increased numbers of common nevi, since dysplastic nevi have been noted to occur specifically in melanoma-prone families [
For counts of large nevi, history of one or more childhood sunburns, and history of one or more lifetime sunburns, RRs were not summarized in the meta-analysis, so a literature search was conducted. Combinations of the following keywords and MeSH terms were used in PubMed: melanoma, etiology, epidemiology, prevention and control, risk factors, case-control studies, cohort studies, cross-sectional studies, nevus, skin pigmentation, skin color, hair color, sun exposure, sunlight, ultraviolet rays, sunburn, suntan, and sunbathing. Included studies were limited to those in English and those examining adult populations. Duplicates, reviews, and irrelevant articles were excluded. Other studies were excluded for ineligible study design (e.g., case series) (14 studies); using outcome of second primary melanoma (11 studies); not being independent of other included studies (3 studies); presenting data by gender, body site, or melanoma subtype (16 studies); or focusing on a restricted age group (1 study). An exception was made for Qureshi et al. and Han et al., as although they are based on the same cohort, the risk factors examined in each are different [
We extracted study location, study design, number and source of cases and controls, age of study population, definitions and categories of risk factors, prevalence estimates, RR or odds ratio (OR) estimates, 95% confidence interval (CI), and variables for which statistical adjustment was done. For articles that presented multiple estimates, we recorded the one adjusted for the most confounders. For risk factors not included in the Gandini meta-analysis, the RR range represents estimates from all included studies, and the median of this range is reported in place of a summary statistic. For other risk factors, the RR range is provided as an update of studies published after 2002.
In order to compare the melanoma rates between Hispanics and NHWs in California, we obtained California population-based risk factor prevalence data wherever possible. The California Health Interview Survey (CHIS) provides information on sunburn prevalence in NHWs and Hispanics [
We used the reported RR for each melanoma risk factor and the risk factor prevalence among Hispanics, to calculate the expected rate of melanoma incidence among Hispanics, and the ratio compared to that in NHWs. We present the rate ratio using an incidence rate of 29 per 100,000 in NHWs (observed in males in California), for which the comparable observed rate ratio is 7.25 (the comparable melanoma incidence rate in Hispanic males in California is approximately 4 per 100,000) [
Because so little data are available on the RR of melanoma risk factors specific to Hispanic populations, we have assumed that the RR in Hispanics is the same as in NHWs (discussed below). Where prevalence of risk factors was unknown in Hispanic populations, we could not calculate the expected rate ratio.
Table
Summary of relative risks (RR) and prevalence of risk factors.
Risk factor | Category |
RR |
95% CI | RR range | Prevalence (%) | Expected rate ratio |
Source | |
---|---|---|---|---|---|---|---|---|
NHW | Hispanic | (Observed = 7.25) | ||||||
Hair color | Blonde | 1.96 | 1.41–2.72 | 0.45–4.13 | 13.60–46.80 | 0.90–3.60 | 1.26 |
Park et al., 2012 [ |
Red | 3.64 | 2.56–5.37 | 1.73–4.94 | 3.10–3.20 | 0.30–1.30 | 1.06 | Park et al., 2012 [ | |
|
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Phototype | Fitzpatrick type I | 2.09 | 1.67–2.58 | 2.36–2.64 | 5.00–7.60 | 1.00–3.30 | 1.04 |
Lin et al., 2012 [ |
Fitzpatrick type II | 1.84 | 1.43–2.36 | 1.82–4.13 | 26.70–39.00 | 10.70–12.00 | 1.16 | Lin et al., 2012 [ | |
Fitzpatrick type I or II | 2.99 | 1.75–5.12 | 1.31–2.90 | 34.30–44.00 | 13.00–14.00 | 1.40 | Lin et al., 2012 [ | |
|
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Freckles | Many freckles | 2.10 | 1.80–2.45 | 1.55–3.72 | 7.43 (controls) | Not available | ~ | |
|
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Nevi | Many nevi | 4.82 | 3.05–7.62 | 1.50–6.50 | 11.66 (controls) | Not available | ~ | |
Many large nevi | 3.05 | 1.19–5.70 | 5.70 | 3.60 | 1.04 | CTP | ||
|
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Sunburn | Many sunburns (lifetime) | 2.03 | 1.73–2.37 | 0.59–8.48 | 7.50–20.70 | 3.80–4.00 | 1.10 | Park et al., 2012 [ |
Many sunburns (childhood) | 2.24 | 1.73–2.89 | 1.00–6.22 | 13.70 (controls) | Not available | ~ | ||
Ever had sunburn (lifetime) | 1.21 | 1.10–5.70 | 61.8 | 21 | 1.08 | Park et al., 2012 [ | ||
Ever had sunburn (childhood) | 1.47 | 0.90–3.56 | 28.19 (controls) | Not available | ~ | |||
|
||||||||
Sun exposure | High total lifetime sun exposure | 1.34 | 1.02–1.77 | 0.80–4.34 | 27.11 (controls) | Not available | ~ | |
High intermittent sun exposure | 1.61 | 1.31–1.99 | 0.65–5.00 | 40.54 (controls) | Not available | ~ | ||
High chronic sun exposure | 0.95 | 0.87–1.04 | 0.33–2.57 | 5.44 (controls) | 12.00 | 1.00 |
Coups et al., 2012 [ |
~Expected rate ratio cannot be calculated because prevalence in Hispanics is unknown.
Most studies comparing rates of melanoma in Hispanics and NHWs focus on delayed diagnosis and overall worse outcomes among Hispanics, while few specifically compare risk factors. Our review confirms that Hispanics do have lower prevalence of some of the major melanoma risk phenotypes, blonde or red hair color, Fitzpatrick skin type I or II, strong history of sunburn, and many large nevi. However, these risk factors are not sufficiently rare in Hispanics to explain their lower rate of melanoma compared to NHWs, largely because there is overlap in the prevalence of the risk factors between Hispanics and NHWs.
Hispanics may have a reduced melanoma risk if they practice better sun protection. Recent studies highlight differences in method of sun protection among subpopulations of Hispanics. Specifically, English-acculturated Hispanics display more sunscreen use but less use of sun protective clothing, while Spanish-acculturated Hispanics are more likely to wear sun protective clothing without sunscreen [
Data from the Behavioral Risk Factor Surveillance System (BRFSS) shows that overall a smaller percentage of Hispanics reported having at least one sunburn in the preceding year compared to NHWs. Hispanics who reported having at least one sunburn in the past year were more likely to have had
A multitude of genetic factors, if substantially different in the two populations, could either protect Hispanics or make NHWs more susceptible to melanoma. Six loci have been implicated in melanoma susceptibility. While five of them represent genes involved in melanin production (
The
The observation that Hispanics have more advanced melanomas at diagnosis than NHWs could be explained by lower awareness of melanoma in this population, resulting in lower likelihood of seeking care [
We make a number of assumptions in our calculations, which are done for illustrative purposes. First, we assume that the RR for each risk factor is the same in Hispanics and NHWs. This is because there is little data assessing melanoma risk factors specifically in Hispanics. It is possible that RRs for melanoma risk factors differ for NHWs and Hispanics but that remains to be shown. For illustrative purposes, we have used incidence data only from NHW and Hispanic males in California, but the rate ratios for comparison among females in California provide similar results. Finally, we considered all invasive melanomas together, though the distributions of the various melanoma histologic subtypes are known to differ between NHW and Hispanics [
To determine effective methods of primary prevention, it is useful to investigate characteristics associated with lower risk of melanoma. To that end, the melanoma experience of Hispanics, who have at least 7-fold lower risk of melanoma than NHWs, might provide clues to improved melanoma prevention. This review highlights the limited data on melanoma risk phenotypes in Hispanic populations; what is currently known about the differences in their prevalence between Hispanics and NHWs inadequately explains a 7-fold difference in melanoma rates.
While genotype may vary between Hispanics and NHWs, there is insufficient data about melanoma risk genes in Hispanic populations to attribute their lower melanoma rates to genetic factors alone. The association between genotype and melanoma risk phenotype might lead us to expect greater differences in skin type and nevi prevalence between Hispanics and NHWs if differentially expressed genetic factors explained the 7-fold difference in melanoma incidence.
While little data exist comparing sun exposure behaviors in Hispanics and NHWs, current data show that Hispanics sunburn less frequently. If sun exposure behaviors help protect Hispanics from melanoma, there could be great potential for improving prevention in all populations through behavioral change. Once the sun exposure behaviors of Hispanics are more clearly understood, prevention messages might be improved. The lower rate of melanoma in Hispanics should be formally investigated in future studies, providing direct comparison of measured risk factors in Hispanics versus NHWs and accounting for any differences in sun exposure behaviors, phenotypic and genotypic characteristics. Such an approach may better inform our methods of melanoma prevention in both Hispanics and NHWs.
The ideas and opinions expressed herein are those of the author(s) and endorsement by the State of California, Department of Public Health the National Cancer Institute, and the Centers for Disease Control and Prevention or their Contractors and Subcontractors is not intended nor should be inferred.
The authors declare that there are no competing interests regarding the publication of this paper.
Dr. Myles G. Cockburn was supported in part by the National Cancer Institute’s Surveillance, Epidemiology and End Results Program under Contract HHSN261201000140C awarded to the Cancer Prevention Institute of California, Contract HHSN261201000035C awarded to the University of Southern California, and Contract HHSN261201000034C awarded to the Public Health Institute and the Centers for Disease Control and Prevention’s National Program of Cancer Registries, under Agreement U58DP003862-01 awarded to the California Department of Public Health.