[Neuroendocrine (Merkel cell?) carcinoma of the skin].
A neuroendocrine carcinoma of the skin was diagnosed in one male and four female patients. Their case histories were short (five months on the average). In two patients, we found metastases of the regional lymph nodes already at the first physical examination; another patient died of distant metastases after 15 months. Histopathological examination revealed cells fairly uniform in size. The tumors replaced the dermis and subcutaneous tissue without affecting the epidermis. In all cases, the cells were arranged in solid sheets and compact nests with occasional cords and trabeculae in the periphery. The cells and nuclei usually were round and hyperchromatic, and showed many mitoses. Typically, the neuron-specific enolase was positive in all tumor formations, whereas the protein S 100 marking was always negative. Electron microscopic examination of the tumor cells showed cytoplasmatic, neurosecretory granules, which were confined to the membranes, as well as collections of perinuclear intermediate filaments and intercellular junctions. A reliable diagnosis regarding neuroendocrine carcinoma of the skin should consider histological, immunohistochemical, and ultrastructural techniques. Cutaneous metastases of other neuroendocrine carcinomas have to be ruled out.