Neuroendocrine carcinoma of the skin with lymphoepithelioma-like features.

We report a case of primary neuroendocrine carcinoma of the skin (PNECS) mimicking a lymphoepithelioma-like carcinoma of the skin (LELCS) with respect to both cytomorphology and the presence of a dense lymphoplasmacytic stroma. The tumor occurred in the left forearm of a 86-year-old woman, and its history was marked by aggressive behavior, with metastases to lymph nodes and to visceral sites within 1.5 years of diagnosis. The neoplastic epithelial cells had an immunophenotypic profile typical of PNECS, reacting for cytokeratin 20 and other low-molecular weight cytokeratins, neuron-specific enolase, neurofilament protein, synaptophysin, and chromogranin A. In addition, they were immunoreactive for epithelial membrane antigen, carcinoembryonic antigen, and S-100 protein, as observed in LELCS of supposed adnexal differentiation. The tumor-infiltrating lymphocytes were mostly of T-lineage, with a predominance of CD8+ cells. We believe the case is a morphologic variant of PNECS, retaining its aggressive behavior and high metastatic potential, and should not be confused with true LELCS, which has a more favorable outcome. Immunohistochemistry is paramount in establishing the diagnosis. Lymphoid infiltration, even if prominent, does not seem to be of favorable prognostic significance in such a context.