Malignant potential of juvenile polyposis coli. Report of a case and review of the literature. Juvenile polyps of the colon and rectum traditionally have been viewed as being benign inflammatory or harmartomatous lesions without potential for malignant change. The authors report a case of adenocarcinoma developing in a patient with sporadic juvenile polyposis. Juvenile polyposis was diagnosed in the patient at age 4 years. He underwent subtotal colectomy at age 6 years. At age 12, he underwent a proctectomy and a Swenson pull-through because of adenomatous changes in the rectal stump. At age 19 surveillance endoscopy revealed invasive cancer in a juvenile polyp. 