Cutaneous metastasis from large-cell neuroendocrine carcinoma of the urinary bladder expressing CK20 and TTF-1.

Large-cell neuroendocrine carcinoma (LCNEC) of the urinary bladder is very rare. Immunohistochemical and biochemical examinations have shown that neuroendocrine carcinomas (NECs) have features of neuroendocrine and epithelial differentiation. We describe the first case of cutaneous metastasis from LCNEC of the urinary bladder. The patient had been treated with partial cystectomy and chemotherapy for LCNEC of the urinary bladder, but a year later, he visited our clinic with a reddish mass on his scalp that was diagnosed as a cutaneous metastasis from LCNEC. The tumor cells were positive for the neuroendocrine markers, cytokeratin (CK) 20 and thyroid transcription factor-1. Most NECs, except for Merkel cell carcinomas, do not express CK20, whereas most urothelial carcinomas do express CK20. These results suggest that a histogenetic link may exist between NEC of the urinary bladder and urothelial carcinoma.