Background: Incidence and mortality of melanoma in the United States have risen steeply. Part of this mortality increase may be related to late detection of biologically aggressive nodular melanomas. We determined trends in distribution of thin and thick melanoma, with emphasis on the histopathologic subtype nodular melanoma.
Methods: Surveillance, Epidemiology, and End Results melanoma incidence data for whites were obtained for 1988 through 1999 and stratified according to histologic subtype: lentigo maligna melanoma, superficial spreading melanoma, nodular melanoma, other, and not otherwise specified (NOS); thickness: 0-0.99 mm, 1.00 mm-1.99 mm, and > or =2.0 mm; patient age (0-49, 50+); gender; and year (1988-1991, 1992-1995, 1996-1999). Comparison of tumor thickness between strata was defined by year of diagnosis, sex, age, and histologic subtype.
Results: The number of new melanoma cases in a 3-year period increased 60% from 1988-1991 (n = 9132) to 1996-1999 (n = 14 575). The proportion of thick melanomas (> or =2 mm) remained relatively stable during the 12 study years. Nodular melanoma comprised 9% of all recorded cases but 34% of melanomas 2 mm or larger, including melanoma not otherwise specified (NOS), and nearly 50% of all melanomas 2 mm or larger when NOS cases were excluded. In contrast, superficial spreading melanoma was almost uniformly diagnosed as an early tumor, mostly (77%) presenting as thin melanoma (<1 mm) and with only 7% presenting as thick melanoma (> or =2 mm).
Conclusions: A substantial number of thick melanomas in the United States are of the nodular subtype, and median thickness of nodular melanoma has not changed during the 12 years of study. New strategies are needed to decrease the incidence of thick melanoma in the United States.