Pathologic tumor and normal mucosa responses after hyperfractionated versus hypofractionated preoperative radiotherapy for rectal cancer.

556 Background: The aim of the study is to assess radiation-induced tumor and normal mucosa responses in patients who underwent preoperative radiotherapy according to two different fractionation protocols. This research constitutes one of the secondary endpoints of a prospective randomized trial. Methods: Pathological samples after preoperative radiotherapy and surgery were obtained from 106 patients: 50 were treated with hypofractionation 39 Gy in 3.0 Gy per fraction (HYPO) and 56 with accelerated hyperfractionation 42 Gy given in two daily fractions of 1.5 Gy with a minimal interfraction interval of 6 hours (HART). This sample represents approximately 30% of an overall trial size. Over 50 pathological features were assessed for each sample including tumor/nodal response, normal mucosa and cellular matrix response, ulceration and morphology of tumor cells. The observed grades of responses in HYPO vs. HART were compared using U Mann-Whitney test. Results: The primary tumor downstaging was observed in 41% ...