¹Division of Cancer Epidemiology and Genetics, National Cancer Institute, Department of Health and Human Services, National Institutes of Health, Rockville, Maryland, USA

Correspondence: Mark P Purdue, E-mail: purduem@mail.nih.gov

TO THE EDITOR

Recent findings suggest that non-melanoma skin cancer incidence in young adults is rising, particularly among US young women (Christenson et al., 2005). This raises the important question of whether incidence of cutaneous melanoma, the most lethal form of skin cancer, is similarly increasing in young adults. Although melanoma incidence among US older adults has been increasing for several decades, there have been indications that incidence may be stabilizing for birth cohorts born after 1945 (Dennis et al., 1993; Hall et al., 1999). However, in an analysis of melanoma trends between 1973 and 1997 in the Surveillance, Epidemiology, and End Results (SEER) Program, Jemal et al. (2001) noted evidence of an increase among women born after 1960. Since that analysis, an additional 7 years of SEER data have been collected. To better understand recent trends in melanoma incidence among young adults, we report findings from a re-analysis of SEER data, extended through 2004.

Our analysis was restricted to Caucasians from the nine registries that have contributed data to the SEER Program since 1973 (Atlanta, Connecticut, Detroit, Hawaii, Iowa, New Mexico, San Francisco-Oakland, Seattle, Utah). We calculated annual age-adjusted incidence (SEER Program, 2007a) and mortality rates (SEER Program, 2007b) of invasive cutaneous melanoma among men and women aged 15–39 years, standardized to the 2000 US population, using the software SEER^*Stat version 6.3.6 (National Cancer Institute; http://www.seer.cancer.gov/seerstat/). We assessed trends in greater detail using joinpoint regression models, which identify changes in trends over successive segments of time and describe the estimated annual percent change (EAPC) in incidence within each segment (Kim et al., 2000), using the software Joinpoint version 3.0 (National Cancer Institute; http://www.srab.cancer.gov/joinpoint/). Joinpoint analyses stratified by melanoma stage (localized vs regional/distant) and thickness (1 vs >1 mm) were also performed. To describe age-specific trends by year of birth, we calculated incidence by 5-year age groups and time periods, and plotted age-specific incidence by calendar year of birth (calculated from the age group midpoint). Additionally, age–period–cohort modeling was used to simultaneously adjust age-specific incidence trends for both calendar period and birth cohort effects (Tarone and Chu, 2000). All P-values were two-sided.

Overall, the age-adjusted annual incidence of melanoma among young men increased from 4.7 cases per 100,000 persons (95% confidence limits: 3.8, 5.7) in 1973 to 7.7 per 100,000 in 2004 (6.8, 8.7). Among women, age-adjusted annual incidence per 100,000 increased from 5.5 (4.5, 6.6) in 1973 to 13.9 (12.7, 15.2) in 2004. Melanoma incidence increased among young men (EAPC=6.6; 95% confidence limits (CL): 2.9, 10.4) and women (9.2; 6.8, 11.7) during the 1970s (Figure 1, Table 1). Around the start of 1980, this pattern changed. For men, incidence leveled off between 1980 and 2004 (0.4; -0.2, 0.9). For women, the rate of increase in incidence declined from 1978 to 1987 (2.6; 1.5, 3.8) and stabilized from 1987 to 1992 (-0.6; -3.7, 2.6). After 1992, however, incidence began increasing again (2.7; 2.1, 3.4). Incidence among women from the 1990s onward increased both for thinner and thicker melanomas (1 mm: 3.1; 2.5, 3.6 and >1 mm: 2.8; 1.6, 4.0), and was greater for regional and distant tumors (9.2; 3.8, 14.9) compared with localized lesions (1.9; 1.6, 2.3). Melanoma mortality rates for men and women declined from 1981 onward (men: -3.6; -4.5, -2.7 and women: -2.3; -3.1, -1.5).

Figure 1.

Trends in melanoma incidence and mortality among young adults. Age-adjusted (to 2000 US population) annual cutaneous melanoma incidence and mortality rates among Caucasian males and females aged 15–39 years in the Surveillance, Epidemiology, and End Results Program areas from 1973 through 2004. The segments of uniform trend from the best-fitting Joinpoint models are also shown.

Full figure and legend (48K)

Table 1 - EAPC in incidence of melanoma and melanoma mortality among Caucasian males and females aged 15–39 years in the SEER Program from 1973 through 2004.

Full table

Age-specific incidence patterns by year of birth are presented in Figure 2. Male age-specific incidence increased steadily with each successive birth cohort until 1950, at which time incidence appeared to level off or decrease slightly. Female age-specific incidence by birth cohort increased steadily until around 1950; thereafter, incidence appeared to climb at a slower pace until 1965, at which point incidence appeared to begin accelerating. After adjustment for age and period effects, age–period–cohort modeling confirmed a change in the effect of birth cohort for women born between 1960 and 1965 (Figure S1; slope change parameter=0.2146; 95% CL: 0.0576, 0.3716; P=0.007).

Figure 2.

Age-specific melanoma incidence among Caucasians stratified by sex and birth cohort year in the SEER program from 1975–1979 through 2000–2004. The points vertically above each cohort year portray the cohort's age-specific incidence experience. The vertical line at 1965 on the x axis of the plot for women represents the time point after which melanoma incidence begins increasing in subsequent cohorts.

Full figure and legend (78K)

It is important to consider whether these trends may reflect changes in data quality, diagnosis, or surveillance. There is evidence of increased underreporting of melanoma over time within the SEER program, with estimates as high as 17% of all cases (including in situ lesions) in two registries, although such a trend in underreporting cannot explain the observed increase in incidence among women (Seiffert, 1992; Merlino et al., 1997). It is unlikely that a change in melanoma diagnostic criteria would account for our finding, because the effect of such a change would not be expected to be sex-specific. Changes in screening patterns may have led to earlier detection within this time period, with a higher rate of increase seen among superficial localized tumors compared with thicker lesions and regional or metastatic disease overall (Jemal et al., 2001; Welch et al., 2005). Indeed, the observed decrease in melanoma mortality rates after 1981 and previously reported evidence of general improvement in survival by stage over this time period are consistent with a shift toward earlier detection of disease through increased surveillance (Jemal et al., 2001). However, in our analysis, the increasing trend among young women from the early 1990s onward was also observed for thicker and regional/distant tumors, which are less susceptible to misclassification. Moreover, our age–period–cohort analysis suggested that, after adjusting for age and period effects (the latter of which is reflective of changes in disease surveillance), the observed increase in incidence among women born after 1965 is consistent with a birth cohort effect (indicative of changes in disease risk factor prevalence across birth cohorts; Tarone and Chu, 2000). Thus, our findings are compatible with a real increase in incidence among young women, although we cannot rule out the effects of changes in surveillance.

The recent increase in incidence among young women parallels reported trends in exposure to UVR, the primary environmental cause of melanoma (Armstrong and Kricker, 2001). The prevalence of sunburn is increasing among US adult men and women overall, although trends by age group have not been reported (Robinson et al., 1997; Saraiya et al., 2007). Among adolescents aged 16–18 years, both the prevalence of sunburn and the average number of days spent at the beach increased between sun surveys conducted in 1998 and 2004 (Cokkinides et al., 2006). Tanning bed usage, which has been recently evaluated as a probable cause of melanoma (International Agency for Research on Cancer, 2007), is increasing among US adults and is most prevalent among young women (Robinson et al., 1997; Lazovich and Forster, 2005).

In conclusion, our analysis of SEER data suggests that melanoma incidence is increasing among young women. Additional studies are needed to clarify whether the increasing trends for melanoma and non-melanoma skin cancer (Christenson et al., 2005) are the result of changes in UVR exposure in this population.