Purpose: To evaluate the extent of distal intramural spread (DIS) after preoperative radiotherapy for rectal cancer.
Methods and materials: A total of 316 patients with T(3-4) primary resectable rectal cancer were randomized to receive either preoperative 5x5 Gy radiation with immediate surgery or chemoradiation (50.4 Gy, 1.8 Gy per fraction plus boluses of 5-fluorouracil and leucovorin) with delayed surgery. The slides of the 106 patients who received short-course radiation and of the 86 who received chemoradiation were available for central microscopic evaluation of DIS.
Results: The length of DIS did not differ significantly (p = 0.64) between the short-course group and the chemoradiation group and was 0 in 47% vs. 49%; 1 to 5 mm in 41% vs. 42%; 6 to 10 mm in 8% vs. 9%, and greater than 10 mm in 4% vs. 0, respectively. Among the 11 clinically complete responders, DIS was found 1 to 5 mm from the microscopically detected ulceration of the mucosa in 5 patients. The discontinuous DIS was more frequent in the chemoradiation group as compared with the short-course group (i.e., 57% vs. 16% of cases, p < 0.001).
Conclusions: Approximately 1 out of 10 advanced rectal cancers after preoperative radiotherapy or radiochemotherapy was characterized by DIS of over 5 mm. No significant difference was seen in the length of DIS between the 2 groups.