Adenocarcinoma Occurring in a Hyperplastic (Metaplastic) Polyp of the Colon

A case of adenocarcinoma occurring in a hyperplastic (metaplastic) polyp of the colon is presented. The polyp, two cm in diameter, was located in the transverse colon of a 45-year-old male patient, and was removed endoscopically. From the periphery to the centre, the polyp showed epithelial changes progressing from hyperplastic to severely dysplastic, terminating in a central focus of invasive adenocarcinoma. It is suggested that the considerable number of absorptive cells in large hyperplastic polyps may occasionally result in an excessive absorption of carcinogen thus leading to dysplastic changes.