Small-cell undifferentiated carcinoma of the colon. A clinicopathological study of five cases and their association with colonic adenomas.

Colonic small-cell undifferentiated carcinoma (SCUC) is an extremely aggressive neoplasm. We describe five patients with colonic SCUC and review five additional, well-documented cases. The longest known duration of survival is 14 months and all patients with follow-up of this duration have died of disease. Regional lymph nodes are invariably involved at the time of diagnosis and when distant metastases were present, the liver was always affected. Four of our cases of SCUC arose in association with colonic adenomas and in two of these the SCUC component was confined to the superficial submucosa. Yet, both produced regional metastases and one had massive hepatic involvement. Ultrastructurally, colonic SCUC exhibits divergent, predominantly neuroendocrine differentiation. The ultrastructural features and association with colonic adenomas suggest an endodermal rather than neuroectodermal derivation.