Quantification of histologic regression of rectal cancer after irradiation: a proposal for a modified staging system.

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Long-course preoperative radiotherapy has been recommended for rectal carcinoma when there is concern about the ability to perform a curative resection, for example, in larger tethered tumors or those sited anteriorly or near the anal sphincter. "Downstaging" of the tumor may occur, and this is of importance when estimating the prognosis and selecting postoperative therapy for patients. We studied the effects of preoperative chemoradiotherapy on the pathology of rectal cancer, and we propose a simplified measurement of tumor regression, the Rectal Cancer Regression Grade. We have reviewed those patients who received preoperative chemoradiotherapy followed by surgical resection for carcinomas of the mid or distal third of the rectum found to be Stage T3/4 on transrectal ultrasound or CT between January 1995 and December 1998. Patients received 45 to 50 Gy irradiation and an infusion of 5-fluorouracil. The surgical specimens were examined by one pathologist, and the Rectal Cancer Regression Grade was quantified. Forty-two patients, mean age 60 (range, 42-86) years, underwent chemoradiotherapy before surgery for rectal carcinoma. There were 28 anterior resections (67 percent; 9 with a colonic pouch), 12 abdominoperineal resections (27 percent), and 2 Hartmann's procedures (5 percent). Comparison of preoperative and pathologic staging revealed that the depth of invasion was downstaged in 17 patients (38 percent), and the status of involved lymph nodes was downstaged in 13 (50 percent) of 26 patients. Tumor regression was more than 50 percent (Rectal Cancer Regression Grades 1 and 2) in 36 patients (86 percent), with 7 patients (17 percent) having complete regression with absence of residual cancer cells. Significant tumor regression was seen in 86 percent of cases after chemoradiotherapy, with 19 patients showing a "good" responsiveness. We propose a modified pathologic staging system for irradiated rectal cancer, the Rectal Cancer Regression Grade, which includes a measurement of tumor regression. The utility of the proposed Rectal Cancer Regression Grade must be tested against long-term outcomes before its value in predicting prognosis and survival can be determined.