Basaloid carcinoma of the colon arising at the splenic flexure

Basaloid carcinomas typically arise in the anal canal and there are only three well-documented cases of this neoplasm reported outside the anal canal, none more proximally than the sigmoid colon. The first occurrence of a basaloid colonic carcinoma arising outside the sigmoid colon, at the splenic flexure, is presented.

A splenic flexure mass was resected from a 54-year-old man with a 3-week history of abdominal discomfort, diarrhoea and weight loss. This tumour, like typical anal canal basaloid carcinomas, was composed of islands of basaloid cells with peripheral nuclear palisading; within many islands there was central necrosis and focal squamous differentiation. Ultrastructural and immunohistochemical studies confirmed the basaloid nature and focal squamous differentiation within this neoplasm. Basaloid carcinoma of the anal canal has been associated with human papilloma virus. Using in-situ hybridization, HPV DNA was not detected in this case.

Outside the anal canal, it has been postulated that basaloid colonic carcinomas may arise from cloacogenic embryologic rests, squamous metaplastic epithelium, or totipotential basal cells. The location and pathological findings of this tumour suggest that this rare colonic neoplasm arises from a totipotential basal cell.