p63 expression as a new prognostic marker in Merkel cell carcinoma.

Background. Merkel cell carcinoma (MCC) is an aggressive neuroendocrine skin tumor, mostly affecting elderly individuals. The histogenesis of this rare tumor as well as its prognostic criteria are a matter of dispute. Methods. An immunohistochemical analysis of markers of proliferation (Ki-67/ MIB-1), neuroendocrine differentiation (chromogranin A and synaptophysin), and basal cell differentiation (p63) was performed in a series of 47 cases of MCC. The significance of pathologic data and of immunoreactivity with different markers was evaluated using the chi-square test. Survival curves were calculated using the Kaplan-Meyer method. The survival difference was estimated using the Wilcoxon or Mantel-Cox test. Results. immunohistochemical evidence of neuroendocrine differentiation and immunopositivity for cytokeratin 20 were observed in all cases, whereas positivity for p63 was detected in approximately half of the cases (25 of 47 cases; 53.2%). Cases that were positive for p63 demonstrated a more aggressive clinical course than those that were negative (Z value of 2.93; P =.0003; hazards ratio of 22.22). Conclusions. Data from the current study indicate that p63 expression is associated with a worse prognosis in patients with MCC and represents a new independent marker of clinical evolution.