Trabecular (Merkel cell) carcinoma arising in the wall of an epidermal cyst.

A trabecular (Merkel cell) carcinoma arising in the wall of an epidermal cyst in a 58-year-old white male metastasized, 17 months after local excision, to an inguinal lymph node. Ultrastructural studies showed polygonal tumor cells with typical dense-core granules. Although squamous-cell carcinoma and other malignant neoplasms have been reported rarely to have arisen in epidermal cysts, a literature search failed to find a precedent for the present case.