Abstract
A 72 year-old man was referred to our hospital for a detailed examination of a recurrent rectal polyp. He had past histories of surgery and radiation therapy for prostate cancer at the age of 66 and endoscopic excision of a rectal polyp at the age of 70. Colonoscopy revealed a semi-pedunculated lesion surrounded by friable mucosa, which was positive under positron-emission tomography-computed tomography. Histopathological examination of the endoscopically excised polyp revealed proliferation of atypical cells, characterized by strong pleomorphic or spindle morphology, which was immunohistochemically compatible with undifferentiated pleomorphic sarcoma. We diagnosed this case as sarcoma presumably associated with radiation proctitis.