Melanoma is the second most commonly diagnosed cancer among adolescents and young adults in the United States,1
although mortality continues to decline as survival improves, particularly among adolescents and young adults.4
The early age at onset of these cancers suggests that early life factors are important. In NHW in particular, melanomas occurring in this age group may represent gene-environment interactions involving excessive, intermittent UVR exposure among susceptible individuals, whereas late-onset melanomas may more often reflect accumulated, lifelong sun exposures in comparatively less susceptible individuals.30,31
The incidence of melanoma was higher in adolescent and young adult females compared with males in all age subgroups and in all racial and ethnic groups examined. This pattern is consistent with other published reports that have looked primarily at melanoma within the NHW adolescent and young adult populations,1
but differs from the pattern of male excess seen at older ages.32
This reversal in the gender RR between younger and older age groups suggests that there may be differences between etiologic pathways in younger versus older age groups that are mediated by gender.
One factor that may be related to this observed age-specific incidence pattern is female sex hormones. Some studies have found that the use of oral contraceptive or hormonal replacement therapy was associated with an increased risk of melanoma,33,34
whereas other studies have not found an association.35,36
Such inconsistent findings may be related to variations in measurement of estrogen receptor expressions.37
Specific genotypes have been found to be related to increased risk of melanoma among young women and may play a crucial role in the development of melanoma.38
In addition, one case-control study has suggested a link between endogenous female hormones related to pregnancy and increased melanoma risk.35
Additional research is needed to further explore possible etiologic pathways and the relationship between longitudinal trends in incidence and fertility rates (ie, delayed childbearing age at first birth and number of full term pregnancies).39
This study, although limited in years of observation, found evidence that incidence rates increased over time among adolescent and young adult females but not males. This finding is consistent with the results from previous studies based on data from the SEER Program, covering between 10% to 14% of the US population.4-6,32
There was a steeper increase in incidence among young females than males and mortality decreased in both groups. An increase in the incidence of melanoma in the presence of declining mortality could be explained by expanded skin screening and detection of biologically indolent tumors with low metastatic potential. However, an analysis of SEER incidence data over a 10-year period showed that increasing melanoma incidence rates occurred in all socioeconomic groups, histologic subtypes, and tumor thickness. The authors concluded that screening associated diagnoses could not explain the increasing incidence of thicker tumors in lower socioeconomic groups with poorer access to screening.40
Historical data on sun exposure in the United States by age are limited. However, one study reported an increase (although not statistically significant) in prevalence of sunburn in age 16 to 18 years from 1998 to 2004.41
Further, the prevalence of sunburn at all ages has continued to increase in both men and women.42
Sunburn has typically been used as one indicator of high intermittent exposure to UVR, the form of sun exposure most strongly related to melanoma risk.13
In addition, there is increasing evidence that artificial sources of UV exposure, including frequent indoor tanning, are associated with melanoma and other skin cancers.12,43,44
Adolescents, especially white adolescent girls, commonly use indoor tanning: up to 37% of NHW female adolescents and 11% of NHW male adolescents have used tanning booths at least once in their lifetimes45,46
and approximately 11% of adolescents report using a tanning bed in the past year.41,47,48
Certain segments of the population, especially teenagers and young adults, view the purported benefits of UV exposure (eg, protective base tan, appearances, feel healthy, and social interactions with friends) as outweighing the risk for skin cancer and effects on their future appearance (wrinkles).49-54
These attitudes are also associated with sporadic sunscreen use and more frequent sunburns.48
In general, melanoma is uncommon in non-whites and Hispanics when compared with NHW populations of all ages.55
The low incidence of skin cancers in darker-skinned groups is primarily a result of photoprotection provided by increased epidermal melanin, which filters twice as much UVR as does that in the epidermis of whites.56
Hence, UVR, the most important predisposing factor for skin cancer in whites, appears to play a lesser role in darker-skinned individuals.
The body site distribution of melanoma in adolescents and young adults differ somewhat from that of older adults. In both sexes, melanomas of the trunk are overrepresented in adolescents and young adults compared with older adults.55
The preponderance of trunk melanomas in this age group–accounting for nearly half (46.7%) of melanomas in males and 37% in females–suggests the importance of intermittent sun exposure, because the trunk is considered a usually unexposed body site, with most exposure in short, intense bursts. The variation in body site distribution across racial/ethnic groups parallels that for all ages, with melanomas on the lower extremities relatively more common in HW and non-white racial groups.55,57
Among the 4 specified histologic types of melanoma, superficial spreading melanoma and nodular melanoma account for the majority of lesions in adolescents and young adults, and occurred in all sites of the body among NHW. This is consistent with other studies that have reported superficial spreading melanomas to be more common among whites and Hispanics.58
Although the numbers are too small to draw any conclusions from these data about differences in the distribution of histologic types across racial/ethnic groups in adolescents and young adults, there is a suggestion that groups other than NHW have an overrepresentation of acral lentiginous melanomas and other specified histologies. This is consistent with findings for all ages that acral lentiginous melanomas, which usually arise on the palm of the hand or sole of the foot, is more common in people of color, especially blacks, compared with white populations.57,59
This observation probably accounts, at least in part, for the excess of melanomas on the lower extremities observed in these groups. In addition, in whites and to a lesser extent, Hispanics, melanomas predominantly occur in sun-exposed skin, whereas in Asians and blacks, UV does not appear to be a significant risk factor, and the majority occurs in non-sun-exposed skin.60
Strengths and limitations
Understanding the burden and relative risk of melanoma among adolescents and young adults is important to developing effective and targeted approaches to reducing incidence and deaths. This study provides a detailed description of melanoma incidence by demographic and tumor characteristics among patients between the ages of 15 to 39 years using data from 38 population-based cancer registries participating in either or both the NPCR and SEER Program and covering 67.2% of the US population.
Population-based cancer registries provide critical information on the cancer burden and the United States is fortunate to have nearly nationwide cancer surveillance coverage. We used only high-quality registry data to mitigate the influence of the under-reporting of incidence cases and the misclassification of demographic and tumor-related data. However, this study is subject to several limitations.
First, incomplete reporting and misclassification of data remain a potential problem in cancer registries. As this study reported, up to 6% cases had unspecified or unknown race/ethnicity data. And routine misclassification of AI/AN as white has led to the systematic underreporting of cancer in the AI/AN population.61
Routine linkage of cancer registry data with Indian Health Service administrative databases for the purpose of classifying race and improved collection and reporting of race information in population estimates26
has resulted in a more accurate estimate of the cancer burden in the AI/AN population,61
including melanomas in AI/AN adolescents and young adults.62,63
Second, more than 50% of all cases were coded with a Histology NOS, thus limiting our ability to look more closely at histologic subtypes including “other” specific histologic types that may differ by age, race, and ethnicity. Primary data reporters (physicians, and laboratory and medical records staff) play a critical role in the ability of the cancer registry staff to collect, consolidate, and report complete, accurate, and specific incidence data. Improved primary data reporting is needed to increase data specificity in the future.
Public health implications
There are important reasons for examining the cancer burden in adolescents and young adults. An examination of incidence patterns in this age group may foretell the future cancer burden, because changing exposure opportunities of early life that can begin to manifest as cancer during adolescence and young adulthood, and provide insight into etiologic relationships as the time since exposure and diagnosis may be somewhat shorter in young adults than for older adults.7,62
In particular, an analysis of melanoma among the young adult population may provide insight into the current and future burden of melanoma in the US population and serve as a critical first step toward describing, monitoring, and eventually eliminating this cancer.
Public health campaigns to promote awareness of the risk of sun exposure in Australia and Europe may have contributed to stabilizing or declining melanoma incidence rates in young adults in those countries. There is increasing awareness of the potential harmful effects of artificial sources of UV exposure particularly among adolescents and young adults. The World Health Organization has designated tanning equipment to be carcinogenic.44
As of June 2011, 26 states had enacted laws restricting minors access to tanning facilities.63
Promoting awareness of the harmful effects of UV exposure (both artificial and natural) and promoting screening for melanoma remain important strategies for reducing the future burden of melanoma in the adolescent and young adult populations. In addition, additional research is required to understand the role of gene-environment exposure interaction and to be able to identify susceptible individuals in the populations that may be at particular risk of developing melanoma.