[The neuroendocrine Merkel cell carcinoma of the skin].

Seven primary skin tumors from 5 women and 2 men were analyzed by light and electron microscopy and immunocytochemistry. The tumors were localized on the face (3 tumors) and on the extremities. The maximum diameter was between 1 and 3.5 cm. Two tumors metastasized to the regional lymph nodes 4 months after excision of the primary, 1 tumor metastasize to the regional lymph nodes after 5 years and the patient died of multiple metastases 8 years after excision of the primary on the forearm. No local recurrences developed. The tumors occurred in the dermis with frequent infiltration of the subcutaneous tissue. The epidermis was intact. The tumor cells formed large solid clusters, while their cytoplasm was faintly basophilic and formed a small rim round the large pale nucleus. In electron microscopy many cells displayed cytoplasmic electron-dense secretory granules with a mean diameter of approx. 100 nm. Immunocytochemistry showed that a large number of cells in all tumors contained neuron specific enolase and many cells of 4 tumors yielded formaldehyde-induced fluorescence. The tumors are therefore of neuroendocrine origin and may derive from merkel cells. They frequently give rise to erroneous diagnosis of metastasis of carcinoma or malignant lymphoma to the skin.