Pathological studies in rectal cancer.

In order to improve our selectivity in treating rectal cancer by local measures alone and to delineate patients most suitable for adjuvant preoperative (abdominoperineal resection) radiation therapy, we have evaluated rectal cancer size, configuration, and grade, and correlated this information with subsequent pathological findings. Data from 247 patients treated by abdominoperineal resection were analyzed. Only 15-20% of exophytic/moderately or well-differentiated tumors had gross transmural invasion, independent of size. Twelve percent of ulcerated/moderately or well-differentiated tumors less than or equal to 4 cm penetrated grossly through the wall, vs. 42% of those greater than 4 cm. Sixty-seven percent of poorly-differentiated or colloid carcinomas greater than 4 cm also had gross transmural penetration. These data suggest patients most likely to benefit from preoperative radiation therapy are those with poorly differentiated or colloid tumors, or with ulcerated lesions greater than 4 cm in size of moderate or well-differentiated histology. All seven exophytic/well-differentiated carcinomas less than or equal to 4 cm, and 4/5 exophytic/moderately differentiated tumors less than or equal to 3 cm had penetration limited to the bowel wall only.