Epidemiology and prognosis of anorectal melanoma

Abstract

Background: The epidemiology of anorectal melanoma has not been well studied despite its potential relevance to the cutaneous melanoma epidemic, and prognostic studies have generally been based on referred cases.

Methods: Data reported to nine population-based registries in the United States during 1973 through 1987 were analyzed.

Results: Fifty-five cases were reported (0.017 x 10(-5)/year). The incidence among blacks was higher but not significantly higher than among whites [relative risk (RR), 1.7; 95% confidence interval (CI), 0.7-3.9]. Registries north of 40 degrees latitude reported higher incidence than registries south of 38 degrees (RR, 3.2; 95% CI, 1.5-7.1). Incidence was higher in women than men (RR, 2.3; 95% CI, 1.2-4.3) and increased steadily with age but did not change over time. Of the 46 (84%) cases with known stage at diagnosis, 37% were confined to the anorectum, 41% had regional spread, and 22% metastasized to distant sites. One and 5-year survivals (+/- SE) were 50% +/- 7% and 15% +/- 6%, respectively. One-year survival for local, regional, and distant disease was 75% +/- 11%, 39% +/- 12%, and 33% +/- 16%, respectively. Prognosis improved over the 15 years of surveillance. Age, sex, race, and registry area were not associated with survival.

Conclusions: Anorectal melanoma differs markedly from cutaneous melanoma in etiology (indeed, sun exposure may be protective) and has a very poor, although improving prognosis.