Our analysis of almost 300 million person-years and over 70,000 new cases of malignant melanoma, the largest such assessment to date, suggests a continued rise in new cases of malignant melanoma in the US. These findings update through 2004 prior reports indicating persistent rises in incidence from the 1960s in the US (Geller et al., 2002
; Ries et al., 2002
) and are consistent with mounting evidence of similar trends worldwide (de Vries et al., 2003a
; de Vries and Coebergh, 2004
; de Vries et al., 2003b
; Koh et al., 2003
; Lasithiotakis et al., 2006
; Mansson-Brahme et al., 2002
; Stang et al., 2006
; Ulmer et al., 2003
). Unlike prior large SEER-based analyses, we were able to assess trends jointly by tumor thickness and SES, which allowed for more precise characterization of thick melanoma trends in populations likely to be unscreened or with limited access to physician screening.
We observed that melanoma incidence increased for both men and women across all categories of tumor thickness, including a significant 3.86% annual increase among the thickest tumors (>4 mm). Interestingly, this increase did not correlate with a disproportionate increase in nodular melanomas, which are characterized by rapid growth and may elude early detection. As with prior reports (Geller et al., 2002
), incidence increases were most dramatic for men aged 65 and older. These observations persisted in analyses accounting for improvements in reporting of tumor thickness. When patients were divided according to neighborhood-level SES, increases were noted in all groups, especially those in the lowest two quintiles. Importantly, the lowest SES group demonstrated the steepest rise in the incidence of thick tumors >4mm.
Mortality from melanoma continued to increase, especially among men aged 65 and older (approximately 2% increase annually), consistent with previous reports (Geller et al., 2002
; Ries et al., 2002
) although mortality rates decreased for men and women younger than 65. For all cancers, age is one of the strongest risk factors, presumably due to accumulating DNA damage over time. Melanoma in the elderly may have a different biology and/or altered host immune response, both of which could contribute to increased incidence and mortality (Balch et al., 2001b
). Regardless, the pattern of dramatic increases in melanoma among persons over 65 in the face of decreasing mortality among younger men and women, is notable.
Some have argued that the rapid rises in melanoma incidence are indicative of a true epidemic on the basis of greater ultraviolet radiation-induced carcinogenesis, while others insist that the apparent trends are an artifact of improved surveillance, diagnostic scrutiny (Welch et al., 2005
), and regular screening (Swerlick and Chen, 1996
) leading to increased diagnosis of thinner tumors with lower or no metastatic potential. Our findings inform this debate by showing persistent increases among more fatal, thick (>4mm) tumors and contest the argument that rising incidence rates are solely attributable to increased diagnosis of thinner tumors.
Increasing incidence of thicker melanomas has been reported in earlier population-based studies (Dennis, 1999
; Geller et al., 2002
) but was not noted in recent regional studies from France (Lipsker et al., 2007
) and Germany (Lasithiotakis et al., 2006
). This discrepancy may reflect variations in patterns of disease presentation or study methodology differences including smaller sample sizes in the European studies. Above and beyond diagnostic surveillance, it is possible that reported trends in melanoma have been influenced by patterns of melanoma reporting to cancer registries. Although it is likely that reporting of thin tumors did improve over time as physicians realized their reporting responsibilities, we did not find evidence of selective over-reporting of thin tumors among persons of higher SES groups. Thus, it is unlikely that reporting patterns explain the SES-specific incidence patterns observed here.
Routine screening for skin cancer is currently recommended by the American Cancer Society (Smith et al., 2007
). However, the proportion of non-Hispanic white adults who reported ever having a physician skin examination in National Health Interview Surveys conducted in 1992, 1998, and 2000 ranges from only 14–21%, and physician screening is rare among those without health insurance (Saraiya et al., 2004
). Our data showing increases in melanoma incidence across all SES groups are consistent with previous reports of melanoma increases by census tract poverty level from 1975 to 1999 (Singh et al., 2003
). However, our findings of increasing incidence in low SES groups, who may have reduced access to health prevention education and practices, suggest a true increase in melanoma burden independent of screening access.
Our observations of modest increases in mortality rates in the presence of dramatic increases in incidence are curious, and are probably not attributable to improvements in survival, treatment or early detection alone. Median survival for late-stage melanoma in the US has not changed appreciably over the past 30 years (Barth et al., 1995
), nor have there been any major innovations in melanoma treatment (Korn et al., 2008
). Although the influence of a stage distribution shift towards thinner, more curable tumors has occurred in recent decades (Geller et al., 2007
), the incidence of thicker melanoma has not declined (Jemal et al., 2001
) as supported by our findings of persistent increases in melanomas of all thicknesses over the study period.
This study provides a comprehensive analysis of the most recent SEER data covering a large segment of the US population. Additional strengths include a more specific classification of ethnicity of non-Hispanic whites, providing precise estimates of risk of melanoma among those at highest risk. Moreover, calculation of SES-specific incidence trends allowed us to examine trends of thicker tumors in a population with poorer access to screening. Complete SES data were available for the state of California; however, this reflected relative SES of the patient’s neighborhood at the time of diagnosis, and therefore may be misclassified with respect to socioeconomic characteristics measured at the individual-level or for time periods prior to diagnosis. SES-specific data was not available outside the state of California.
Incomplete reporting of certain cancer registry data items, including histologic subtype and thickness, may have biased the ultimate representativeness of our final study cohort. This issue underscores the dependence of accurate melanoma surveillance on both the quality and completeness of melanoma reporting to cancer registries by diagnosing hospitals and physicians (Hall et al., 2003
). Under-reporting (Koh et al., 1992
; Zippin et al., 1995
; Cockburn et al.
2008, in press) and delayed reporting (Clegg et al., 2002
) of melanoma to cancer registries have been documented and indicate that even the best assessments of melanoma incidence patterns likely represent underestimates.
We do not believe that improvements in the reporting of thickness information over time could fully explain our observations of increasing incidence trends across all thickness categories, as demonstrated in our sensitivity analyses described above. Furthermore, missing thickness was not associated with patient age, sex, or suggesting that thickness data is largely missing at random.
The absolute magnitude of melanoma incidence in older white men warrants greater public health attention, as these data suggest a contemporary incidence rate exceeding 125 cases per 100,000 men aged 65 and older. This is proportional to the incidence of non-Hodgkin’s lymphoma in the same population, making malignant melanoma the 5th
most common cancer in older white men following prostate, lung, colorectal and bladder cancer. If melanoma is truly increasing in all thickness categories and across socioeconomic levels, it will soon become a major concern for an increasingly aging population and their health care providers. Secondary prevention through early detection of melanoma is especially important in reducing mortality in high-risk groups (Geller et al., 2006
), including those of lowest SES who demonstrated the sharpest rises in thick melanoma incidence in the California data. Our analysis also highlights the need for continued, detailed surveillance of melanoma occurrence, which in turn, underscores the importance of complete and accurate reporting of all melanoma cases by hospitals and private physicians.