Affiliation of authors: Division of Cancer Epidemiology and Genetics, National Cancer Institute, Bethesda, MD.
Correspondence to: Ahmedin Jemal, Ph.D., D.V.M., National Institutes of Health, 6120 Executive Blvd., EPS 8049, Rockville, MD 20892 (e-mail: jemala{at}exchange.nih.gov).
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ABSTRACT |
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INTRODUCTION |
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METHODS |
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We also fitted a formal ageperiodcohort model (11) to these data to evaluate changes in the slope of incidence trends by birth cohort. The change in the slope (C) was quantified by use of the identifiable parameter (12,13) centered on birth-cohort j as defined by
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where j denotes the birth-cohort effect identified by birth-cohort j. This parameter compares two linear contrasts, the first contrast characterizing the slope of the birth-cohort curve for the later birth cohorts (j to j + 3) and the second characterizing the slope for the earlier birth cohorts (j 3 to j). A negative value for this parameter indicates a decrease in the birth-cohort slope around cohort j.
Melanoma cases were categorized into three defined tumor stages: local, regional, and distant (2). Local stage indicates that the cancer is confined to the skin as the primary site, regional stage indicates that the cancer involves regional lymph nodes, and distant stage indicates that the cancer has spread to other organs of the body from its primary site. To examine historic and more recent trends of melanoma by these tumor stages, rates age-adjusted to the 1970 U.S. standard population were computed for age groups: under 40 years, 4059 years, 60 years and older, and all ages combined for grouped (and averaged) calendar years from 19741975 through 19881989 and from 19901991 through 19961997. Estimated annual percent changes (EAPCs) were calculated by fitting a regression line to the natural logarithm of the age-adjusted rates, weighted by the inverse of the estimated variance of the logarithm of age-adjusted rates, using the calendar year as the predictor variable, i.e., y = bx + a, where y = ln (rate), x = calendar year, and a = constant; then the EAPC = (eb 1)*100. The coefficients, b, were tested for being different from zero by use of the two-sided Student's t test at P<.05 significance level (14).
Information on tumor thickness in the SEER database is available for cases diagnosed since 1988 (15). We categorized invasive melanoma cases according to their thickness into less than 1 mm, 1 to less than 4 mm, and greater than or equal to 4 mm. Then we computed the annual age-adjusted rates from 1988 through 1997 by thickness for all primary lesions for age groups less than 40 years, 4059 years, 60 years and older, and all ages. We also computed the age-adjusted rates by thickness for only the first primary melanoma. The EAPCs for all primaries were calculated by following the method described above.
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RESULTS |
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Table 2 shows the sex-specific melanoma trends by age groups and by tumor thickness from 1988, the first year that this information was available, through 1997. For all ages combined, rates increased statistically significantly (P<.05; see Table 2
for individual P values) for every thickness category except for thick tumors (
4 mm) among females. Rates increased more rapidly in males than in females and more so for thick tumors. For ages under 40 years, the only upward trend among males was in thin tumors; intermediate and thick tumors showed downward trends. However, none of these trends were statistically significant (P>.05). Among females under 40 years old, in contrast, all trends were upward but were statistically significant increased only for thin melanoma (<1 mm). For ages 4059 years, rates among males increased statistically significantly for all thickness categories except thick tumors. Among females, in comparison, rates increased statistically significantly for thin tumors, while they decreased nonsignificantly for thick tumors. In ages 60 years and older, rates rose for all thickness categories, except thick tumors among females. Analyses of these data for all tumors and for first primary tumors showed that rates for only first-counted primary tumors and for all primary tumors counted were nearly equal within each tumor-thickness category (data not shown). Second primary tumors accounted for 4% of the total counts in the thin (<1 mm) and unknown tumor thickness categories and for 2% in the thick tumor category (
4 mm). The proportion of unknown thickness categories for all ages combined decreased from 27.2.% in 19881989 to 18.3% in 19961997 among males and from 22.0% to 16.2% among females for comparable time periods. Rates declined for each sex- and age group-specific unknown-thickness category (data not shown).
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DISCUSSION |
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The elevated birth-cohort risks before 1950 were consistent with previous findings (16), while the increased birth-cohort risks after 1960 among females were unexpected, since prior reports (16,17) suggested stabilized or declined rates for cohorts born after 1950. Although long-term data on sun-exposure behaviors and attitudes in the United States are unavailable to relate them with birth-cohort risks, it has been suggested that the birth-cohort risks of melanoma are the results of sun-exposure behaviors and attitudes of each generation of males and females during childhood and adulthood (8,17). Robinson et al. (18) reported on trends in sun-exposure knowledge, behaviors, and attitudes in the United States on the basis of analysis of survey data from two time periods, 1986 and 1996. The proportion of people who experienced at least one sunburn, the most consistently associated sun-exposure variable with melanoma (19), statistically significantly increased from 30% in 1986 to 39% in 1996. However, data were inadequate to evaluate differences by birth cohort.
The birth-cohort incidence patterns for females born after 1960 were different from the mortality patterns; mortality consistently declined in cohorts born after 1950 (8,17). The birth-cohort mortality patterns in the SEER areas were generally similar to the national birth-cohort mortality patterns (data not shown), with declines among recent cohorts. Increasing melanoma incidence in the face of declining mortality was reported in New Zealand (20), in England (21), and in a number of other European countries (22). Possible factors contributing to the divergence of incidence and mortality rates include changes in diagnostic criteria and improvement in survival. However, there appeared to be little change over time in histopathologic criteria in the diagnosis of melanoma (23,24).
Survival rates for patients with melanoma increased over time in all age groups in the SEER areas (2). For cases diagnosed between 19741975 and 19921993, the 5-year relative survival increased from 84.5% to 91.5% for ages under 40 years, from 79.4% to 87.51% for ages 4059 years, from 73% to 88% for ages 60 years and older, and from 79.2% to 88.2% for all ages combined. Furthermore, survival for all ages and sexes combined has changed from 89.1% to 95.6% after localized disease, from 56.5% to 59.5% after regional disease, and from 14.0% to 10% after metastatic disease. The general improvement in survival may be related to greater awareness of melanoma by health professionals and the general public, leading to the detection of the disease at an earlier stage. From 19741975 through 19881989, upward trends for rates of local-stage tumors with simultaneous downward trends for distant-stage tumors were seen in ages under 40 years (Table 1). This may partly explain the divergence of incidence and mortality among the young birth cohorts. For the older-aged groups, improvements in survival may have contributed to the moderation of the slopes in mortality.
Our analysis of the incidence data by tumor stages and thickness categories agreed with previous reports (25,26). Between 19741975 and 19881989, overall rates increased statistically significantly (P<.05) for every tumor stage among males and for only local-stage tumor among females (Table 1). In the more recent time period, however, the overall rates increased statisticaly significantly for local- and regional-stage tumors among males but not among females. In general, age-specific rates among males stabilized or declined less for distant-stage tumors for those aged under 60 years and increased more for those aged 60 years and older compared with females. Rates statistically significantly increased for all thickness categories except for the thick lesions among females (Table 2
). Because of lower survival rates of patients with distant-stage and thick tumors (27), the preceding trends may explain why overall mortality from melanoma in the United States is still increasing among males but is stabilizing or declining among females. It is also worth noting that improved detection and documentation of tumor thickness, as reflected on proportional reductions in unstaged and unknown thickness categories over time, to some extent may have contributed to the increased incidence in local-stage and thin lesions.
Many reviewers have examined whether improved detection or real occurrence or both have led to the increase in melanoma incidence (8,25,28,29). Earlier detection, resulting mainly from increased awareness by health providers and the general public, has indeed had an impact, as seen in the higher rate of increase in localized tumors compared with regional and metastatic diseases. However, on the basis of our findings and others, there is supporting evidence to suggest that the trends reflect real changes more than increased diagnosis: 1) Incidence increased more rapidly in the 1970s when there was little awareness of melanoma; educational programs to enhance early detection of melanoma at the national level started in 1985 (30). 2) Sun exposure as measured by sunburning and regular use of a tanning booth increased in the past decade (18). 3) In the time period covered by our analyses, 19741997, the rise in incidence was not limited to local-stage and thin tumors, with potential misclassifications; distant-stage and thick tumors, with little misclassification, also increased statistically significantly (Fig. 4; Tables 1 and 2
). 4) Most important, mortality increased for decades (8,17,25), and there was no major change in the International Causes of Death code for melanoma (31) to account for its increase. 5) It is also noteworthy that melanoma is increasingly diagnosed in nonhospital medical settings, with underreporting as high as 20% of the total cases in some cancer registries (32,33). This, if it did not underestimate the recent trend, may potentially offset misclassification of nevi as invasive melanoma that may have occurred.
In summary, the recent melanoma trends in the United States may reflect increased sun exposure more than increasing diagnosis. Incidence likely will continue to increase, at least until the majority of the current middle-aged population becomes the oldest population. The rise of risk in the more recent birth cohort calls for increased support for primary and secondary prevention programs. However, the current decline or stabilization of rates in distant-stage and thick tumors in males less than 60 years of age may be early indications for peaking of mortality among males in the near future, since it has already been seen among females.
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NOTES |
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We thank Dr. Robert Tarone of the National Cancer Institute (Bethesda, MD) for his advice on data analyses.
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Manuscript received September 18, 2000; revised February 20, 2001; accepted February 28, 2001.
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