A 78-year-old man was admitted to the hospital because of a stricture of the sigmoid colon.Five years earlier, a rectal mass had been found on a routine sigmoidoscopic examination. An examination with a flexible sigmoidoscope showed a sessile, slightly lobulated, polypoid mass, 3 cm in diameter, just within the anal sphincter. Microscopical examination of biopsy specimens suggested a solitary rectal ulcer. The carcinoembryonic antigen level was 1.2 m g per liter. A transanal excision of the mass was performed, and microscopical examination of the specimen confirmed the diagnosis of a rectal ulcer. Follow-up examinations with a flexible sigmoidoscope during the next two months showed complete healing of the surgical site.Four years before admission, an abnormality was felt in each prostatic lobe. The prostate-specific antigen level was 13.9 ng per milliliter. Microscopical examination of a biopsy specimen of the tumor revealed an adenocarcinoma, Gleason grade 3 (on a scale of 1 to 5). A computed tomographic (CT) scan of the abdomen showed three cyst-like low-attenuation foci in the liver, the largest of which was 2 cm in diameter, as well as a solitary left para-aortic lymph node, 9 mm in diameter, and scattered diverticula in the sigmoid colon. A radionuclide bone scan was normal. The tumor was treated with a total dose of 6840 cGy. The patient subsequently began to pass one to four stools daily, either solid or liquid. One year later, he began to note fresh blood with his stools, mainly on the toilet tissue. Anoscopic examination showed small external hemorrhoids. Examination with a flexible sigmoidoscope to the level of the splenic flexure showed moderate diverticulosis.Seventeen months before admission, the prostatespecific antigen level was 4.0 ng per milliliter. Monthly injections of leuprolide were started.Seven months before admission, the patient began to experience fatigue and intermittent lower abdominal cramps and to pass 5 to 10 semisolid daily stools with small amounts of fresh blood. The prostate-specific antigen level was less than 0.5 ng per milliliter. Five and a half months before admission, a CT scan of the abdomen (Fig. 1) showed thickening of the sigmoid colon, adjacent stranding, sigmoid diverticula, and para-aortic and left iliac lymphadenopathy. The largest lymph nodes were 2 cm in diameter. One month later, an examination revealed mild lower abdominal tenderness. A rectal examination showed blood-stained mucus, and an anoscopic study showed small internal hemorrhoids. An attempted colonoscopic examination revealed a fixed, irregular sigmoid stricture that prevented further passage of the endoscope. Moderate mucosal atrophy and telangiectases were seen low in the rectum. Microscopical examination of multiple biopsy specimens showed mild distortion of the glandular architecture and severe chronic inflammation of the muscularis mucosa. Four months before admission, the prostate-specific antigen level was less than 0.5 ng per milliliter. A barium-enema examination (Fig. 2) showed a long sigm...