Adenocarcinoma arising in a traditional serrated adenoma of the rectosigmoid colon with osseous metaplasia.

Within the gastrointestinal tract, osseous metaplasia is an extremely rare phenomenon. It has only recently been described within a traditional serrated adenoma. Serrated colorectal carcinoma is the end point of the serrated neoplasia pathway. Left sided lesions typically arise from traditional serrated adenomas and represent only 8% of colorectal carcinomas. Herein reported is a case of colorectal adenocarcinoma arising from a traditional serrated adenoma with the rare occurrence of osseous metaplasia within the adenoma. The significance of the finding is discussed.