Transformation of Merkel cell carcinoma to ganglioneuroblastoma in intracranial metastasis.

Merkel cell carcinoma is an aggressive neuroendocrine tumor occasionally demonstrating aberrant differentiation to other epithelial and nonepithelial cell lines. We describe a case of Merkel cell carcinoma displaying unique patterns of differentiation in the primary focus and brain metastasis. The skin primary was almost uniformly small cell carcinoma positive for epithelial and neuroendocrine markers, with a few glial fibrillary acidic protein- and cytokeratin 20-positive cells.