Primary small cell carcinoma of skin. Histogenetical study.

Four cases of primary small cell carcinoma of the skin (PSCCS) are presented (ages ranging from 60 to 68 years). Ultrastructurally, two cell types were identified, with both presenting electron-dense secretory granules and paranuclear intermediate filaments. Argyrophylia was positive in one case. Intense solar elastosis in two cases and actinic keratosis in one case suggest a possible role from solar damage in the pathogenesis of this tumor. According to comparative ultrastructural features, different histogenetic possibilities in Merkel cells (MC), peripheral neuroblastic tissue, and totipotential cells are discussed. Some neurosecretory-like granules were observed in basal cell carcinoma (BCC). We consider that PSCCS reproduces cells similar to MC and probably originates in stem cells with totipotential capacity.