SMALL-CELL CARCINOMA ARISING FROM THE OUTER URETHRAL ORIFICE - A CASE-REPORT EXAMINED BY HISTOLOGIC, ULTRASTRUCTURAL AND IMMUNOHISTOCHEMICAL METHODS

A case of small cell carcinoma arising in the outer urethral orifice i s presented. The resected tumor showed a proliferation of small round or fusiform neoplastic cells in the submucosa. Tumor cells were arrang ed in sheets or a trabecular manner and possessed markedly hyperchroma tic nuclei with a high N:C ratio, closely resembling small cell carcin oma of the lung. Characteristically, pagetoid intraepithelial spreadin g could be identified. However, there was no evidence of in situ trans itional cell carcinoma and adeno- or squamous cell carcinoma component s anywhere. Ultrastructurally, each tumor cell contained only a few me mbrane-bound cored granules measuring 60-100 nm, which were compatible with neurosecretory granules, and desmosome-like intercellular attach ments, but lacked aggregated microfilaments. By immunohistochemical ex amination, tumor cells were positive for epithelial markers, such as c ytokeratin and epithelial membrane antigen, and neuron specific enolas e, but negative for any other neuro-endocrine markers. Extensive syste mic examination failed to show the primary site to be other than the o uter urethral orifice. These findings indicate that the current tumor is a small cell carcinoma with neuro-endocrine differentiation arising from the outer urethral orifice.