Implications of precancerous rectal biopsy in patients with inflammatory bowel disease.

Sixty-five patients with an initial diagnosis of ulcerative colitis who underwent total proctocolectomy between 1955 and 1973 were studied retrospectively. Rectal mucosa in each patient was examined microscopically for the presence or absence of "precancerous" alterations as described by Morson and Pang. Histologic examination was made with no knowledge of concomitant colon carcinoma or the patients' clinical courses. Three of ten patients with precancerous rectal mucosa had invasive colon carcinoma, while none of the 55 patients without such changes had colon cancer (P less than .05, Fischer exact test). The duration of disease was significantly greater in those patients with rectal precancer (P less than .05). Reexamination changed the pathologic diagnosis in 15 patients from ulcerative colitis to granulomatous or "mixed" colitis. Two of three invasive cancers occurred in the reclassified group. Results support previous contentions that careful histologic evaluation of rectal biopsy specimens from individuals with inflammatory bowel disease may better define that population of patients with an increased risk of colonic carcinoma.