Merkel cell carcinoma: molecular pathogenesis, clinical features and therapy.

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine carcinoma of the skin. The incidence of this rare tumor is increasing rapidly; the American Cancer Society estimates for 2008 almost 1500 new cases in the U.S. Thus, the incidence of MCC will exceed the incidence of cutaneous T-cell lymphoma. Moreover, the mortality rate of MCC with 33% is considerably higher than that of cutaneous melanoma. These clinical observations are especially disturbing as we are only recently beginning to understand the pathogenesis of MCC. For the same reason, the therapeutic approach is often unclear; reliable data are only available for the therapy of locoregional disease.