Is step section necessary for determination of complete pathological response in rectal cancer patients treated with preoperative chemoradiotherapy?

Aims: To assess the efficacy of the step section for determination of pathological complete response (pCR) in rectal cancer treated with preoperative chemoradiotherapy (CRT). Methods and results: Of 709 patients with rectal cancer who received preoperative CRT, 88 were initially diagnosed as having pCR. These 88 patients were re-evaluated after two-level step sections of the entire tumour by using Dworak's regression grade. Additional serial step sections revealed residual tumour cells in seven of 88 patients (7.95%), all of whom were upgraded to regression grade 3 (near total regression) from regression grade 4 (total regression). Of these seven patients, one (14.3%) showed tumour recurrence, compared with 11 of 81 (13.6%) patients with a final regression grade of 4. Neither recurrence rate nor disease-free survival rate differed significantly between these two groups (P > 0.5). Calcification was significantly more frequent in grade 3 than in grade four patients (71.4% versus 32.1%; P = 0.037), and acellular mucin pools were associated with better disease-free survival (P = 0.022). Conclusions: Stratifying patient outcome by final regression grade after step section did not yield different outcomes in patients with initial pCR. If residual tumour cells are not identified on initial meticulous examination, further processing of step sections is not necessary.