Association between neuroendocrine (Merkel cell) carcinoma and squamous carcinoma of the skin.

Among 32 neuroendocrine carcinomas of the skin, 11 were from patients with previous or concomitant squamous carcinoma. The medical records and pathologic material for these 11 cases were reviewed, and the diagnosis of neuroendocrine carcinoma was confirmed in each instance by electron microscopy. In two cases, the squamous and neuroendocrine carcinomas were admixed, but each preserved its identity and transition between the two was not identified. Despite the lack of evidence for origin from a single cell, the observations nevertheless indicate a common carcinogenetic influence for squamous and neuroendocrine carcinomas of the skin.