Basaloid carcinoma of the colon arising at the splenic flexure

Aims: Basaloid carcinomas typically arise in the anal canal and there are o nly 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 spl enic flexure, is presented. Methods and Results: A splenic flexure mass was resected from a 54-year-old man with a 3-week history of abdominal discomfort, diarrhoea and weight lo ss. This tumour, like typical anal canal basaloid carcinomas, was composed of islands of basaloid cells with peripheral nuclear palisading; within man y islands there was central necrosis and focal squamous differentiation. Ul trastructural and immunohistochemical studies confirmed the basaloid nature and focal squamous differentiation within this neoplasm, Basaloid carcinom a of the anal canal has been associated with human papilloma virus. Using i n-situ hybridization, I-IPV DNA was not detected in this case. Conclusions: Outside the anal canal, it has been postulated that basaloid c olonic carcinomas may arise from cloacogenic embryologic rests, squamous me taplastic epithelium, or totipotential basal cells. The location and pathol ogical findings of this tumour suggest that this rare colonic neoplasm aris es from a totipotential basal cell.