Squamous cell carcinoma of the ascending colon.

A right-sided colon lesion appearing as a typical adenocarcinoma was biopsied and revealed squamous cell carcinoma. The etiologic possibilities include metastatic disease to the gastrointestinal tract (most likely from the lung in this case) and the very uncommon primary squamous cell carcinoma of the colon. The described features of both lesions are reviewed.