Presence of distal intramural spread after preoperative combined-modality therapy for adenocarcinoma of the rectum: what is now the appropriate distal resection margin?

Background: Preoperative combined-modality therapy (CMT) is considered the treatment approach of choice for rectal cancer. To examine the effect of CMT on distal intramural spread (DIS), we determined the extent of DIS in rectal cancer specimens after CMT.
Methods: Specimens from 20 patients after preoperative CMT and total mesorectal excision for rectal cancer were analyzed for extent of DIS. Specimens were washed, fixed in formalin, and sectioned in 5-mm cuts from the distal border of the residual tumor to the distal resection margin.
Results: Eleven patients (55%) had DIS. Two patients had a complete pathologic response (10%). The mean extent of DIS was 0.50 cm (standard deviation, 0.64 cm; range, 0.0 to 2.5 cm). Only 1 patient in the study had DIS beyond 1 cm from the residual tumor. Six of the patients have died at a median of 30.4 months after operation (range, 19.0 to 51.1 months). No correlation was found between the extent of residual DIS and survival.
Conclusions: Our study shows that the vast majority of patients with rectal cancer after neoadjuvant CMT have no tumor cells beyond 1 cm from the residual tumor. Our data suggest that a 2-cm margin of resection when feasible from the macroscopic tumor margin after neoadjuvant CMT is adequate.