Merkel cell carcinoma: histologic features and prognosis.

BACKGROUND: Currently, little is known regarding the potential prognostic value of histologic features in primary cutaneous neuroendocrine (Merkel cell) carcinomas (MCC).

METHODS: In a retrospective review of the tumor histology and clinical outcome data (median follow-up, 51 months; range, 3-224 months) of 156 patients with a diagnosis of MCC, the following histologic features were evaluated: tumor thickness, tumor size (greatest dimension of the tumor), microanatomic compartment involved by tumor (dermis and/or subcutis and/or deeper), tumor growth pattern (nodular circumscribed vs infiltrative), lymphovascular invasion (LVI), tumor-infiltrating lymphocytes, tumor necrosis, ulceration, and solar elastosis.

RESULTS: The overall 5-year survival rate was 67.5%. On univariate analysis, parameters that were associated significantly with survival were tumor thickness (P= .001), tumor size (P= .0002), deepest anatomic compartment involved by tumor (P= .0003), tumor growth pattern (P= .003), LVI (P< .00001), tumor-infiltrating lymphocytes (P= .05), and solar elastosis (P= .04). On multivariate analysis, the presence of a nodular growth pattern, low tumor depth, and absence of LVI were associated with longer survival.

CONCLUSIONS: In addition to the known prognostic value of tumor stage, 3 histologic features were identified to have prognostic significance: tumor thickness (depth of tumor invasion), the presence of LVI, and tumor growth pattern.