A Case of Mixed Hyperplastic-adenomatous Rectal Polyp with Composition of Invasive Adenocarcinoma

Epithelial colon polyps are largely divided into hyperplastic and adenomatous polyps. Adenomatous polyps are premalignant lesions, whereas hyperplastic polyps are regarded as benign lesions. However, this histological classification has been blurred, as cases of malignant changes in hyperplastic polyposis, mixed hyperplastic adenomatous polyps (MHAPs), and serrated adenomas in the colon have been reported. Rare cases of MHAP have been reported, and are mainly found at the proximal colon with a relatively large size. MHAPs seem to be an intermediate stage of the hyperplastic polyp-adenoma sequence or a collision tumor. Here, we report on a case of a single polyp in the rectum diagnosed with a MHAP combined with an invasive adenocarcinoma.