Epidemiology and prognosis of anorectal melanoma.

Abstract

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. Data reported to nine population-based registries in the United States during 1973 through 1987 were analyzed. 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. Anorectal melanoma differs markedly from cutaneous melanoma in etiology (indeed, sun exposure may be protective) and has a very poor, although improving prognosis.