Deletion of chromosome arm 1p in a Merkel cell carcinoma (MCC).

A case of neuroendocrine skin carcinoma (Merkel cell carcinoma) with a deletion of the short arm of chromosome 1 (1p) as the sole chromosomal abnormality was examined. The tumor originated in the skin of the left knee of a 67-year-old man. Histopathologic study showed an undifferentiated small cell tumor which expressed neuron-specific enolase, chromogranin, and cytokeratin (CAM 5.2). Cytogenetic analysis of a lymph node metastasis from the groin showed a pseudodiploid cell population with a deletion of the short arm of chromosome 1 as the only abnormality: 46,XY,del(1)(p36.1). In situ hybridization with the D1Z2 probe specific for the terminal band of 1p confirmed the terminal deletion. This is the first case of Merkel cell carcinoma in which only one chromosomal abnormality has been observed. Loss of the terminal portion of 1p suggests that a tumor suppressor gene on 1p plays a role in the pathogenesis of Merkel cell carcinoma.