Distal intramural and tumor spread in the mesorectum after neoadjuvant radiochemotherapy in rectal cancer: about 124 consecutive patients

Abstract This observational prospective study aimed to assess the distribution of intramural and mesorectal tumor spread in mid/low rectal cancer after neoadjuvant radiochemotherapy (RCT). Distribution of mesorectal metastatic lymph nodes (MLNs) and mesorectal extranodal cancer tissue (EX), according to the tumor location, were analyzed. Distal intra-mural tumor spread was also performed. A total of 1676 LNs, 135 MLNs and 69 EX were detected on 124 consecutive surgical specimens. Forty two patients (34 %) had MLNs. Six patients (4.8%) were classified as ypN1c. Distal viable cancer spread was observed in 3 patients (2.4%), all with mid rectal carcinoma. Two patients (1.6%) presented distal direct intra-mural extension less than 1cm and one (0.8%) with EX localized no more than 2cm from the lower edge of the tumor. MLNs (76%) and EX (94%) were preferentially localized in the peritumoral area and in the 3 first centimeters just above the tumor. No viable distal intramural or mesorectal spread was observed in low rectal carcinoma. Distal intramural and mesorectal cancer spread is a rare event after neoadjuvant CRT. These results suggest that the 1cm distal margin recommended in patients with low rectal carcinoma could be reduced with insurance to obtain a negative distal margin. The knowledge of preferential localization of MLNs and EX would help the pathologist to improve patient's lymph node staging.