Morphologic changes in primary neuroendocrine carcinoma of the skin following radiation therapy

A case of primary neuroendocrine carcinoma of the skin (NECS) treated by radiation therapy is reported. Biopsy prior to irradiation showed a tumor with the characteristic light microscopic, immunohistochemical, and ultrastructural features of NECS. Following external beam irradiation, 6,000 rad, the size of the lesion decreased markedly. Examination of the excised residual mass revealed dense fibrous connective tissue with entrapped nests of large tumor cells that differed markedly from those in the previous biopsy specimen. The neoplastic cells in the excised mass had abundant, vacuolated, eosinophilic cytoplasm and pleomorphic nuclei. In spite of these marked morphologic alterations, the original immunohistochemical phenotype was retained. These observations suggest that radiation may induce profound histologic changes in NECS.