Merkel cell carcinoma and melanoma: Etiological similarities and differences

Merkel cell carcinoma (MCC) of the skin and cutaneous malignant melanoma ca n now be compared epidemiologically through the use of population-based dat a not previously available for MCC, The results may provide new clues to et iology, In this study, United States data covered by the Surveillance, Epid emiology, and End Results (SEER) Program were from nine areas of the United States (similar to 10% of the population). In 1986-1994, 425 cases of MCC were registered. The annual age-adjusted incidence per 100,000 of MCC was 0 .23 for whites and 0.01 for blacks; among whites, the ratio of melanoma to MCC was similar to 65 to 1. Only 5% of MCC occurred before age 50, unlike t he lifelong risk of nodular and superficial spreading melanoma, Regional in cidence rates of both cancers increased similarly with increasing sun expos ure as measured by the UVB solar index. The most sun-exposed anatomical sit e, the face, was the location of 36% of MCC but only 14% of melanoma, Both cancers increased in frequency and aggressiveness after immunosuppression a nd organ transplantation (36 cases from the Cincinnati Tranplant Tumor regi stry and 12 from published case reports) and after B-cell neoplasia (5 case s in this study; 13 from case series in the literature). The SEER data cont ained reports of six patients with both types of cancer; 5 melanomas before the diagnosis of MCC and 1 after diagnosis, MCC and melanoma are similarly related to sun exposure and immunosuppression, but they differ markedly fr om one another in their distributions by age, race, and anatomical site, es pecially the face.