Neoadjuvant chemoradiotherapy is associated with prolonged relapse free survival in patient with MRI-detected extramural vascular invasion (mrEMVI) positive rectal cancer: A multicenter retrospective cohort study in Japan.

Purpose: Neoadjuvant chemoradiotherapy (nCRT) is employed for the local control of locally advanced rectal cancer; however, its prognostic impact is limited and often impairs pelvic organ function. Therefore, careful patient selection is essential. This study aimed to investigate the impact of nCRT on relapse-free survival (RFS) by stratifying patients according to MRI detected circumferential resection margin (mrCRM) or extramural vascular invasion (mrEMVI), as the ability of MRI findings to identify patients who will have beneficial outcomes from nCRT is uncertain.

Methods: We retrospectively analyzed patients with clinical stage II-III lower rectal cancer who underwent surgical resection with or without nCRT between 2010 and 2011 at 69 hospitals in Japan. The impact of nCRT on RFS was evaluated using multivariable Cox regression models in the entire cohort and in subgroups stratified by mrCRM or mrEMVI status.

Results: In the entire cohort (nCRT, n = 172; surgery alone, n = 503), nCRT showed a trend toward improved RFS, although the difference was not statistically significant (HR, 0.74; 95 % CI, 0.54-1.03; P = 0.074). Among mrCRM-negative and mrEMVI-negative patients, there were no significant differences in RFS between the nCRT and surgery-alone groups. Among mrCRM-positive patients, nCRT tended to improve the RFS (HR, 0.70; 95 % CI, 0.46-1.06; P = 0.089). Among mrEMVI-positive patients, nCRT significantly prolonged the RFS (HR, 0.62; 95 % CI, 0.38-1.00; P = 0.048).

Conclusions: Compared to surgery alone, nCRT did not significantly improve RFS in the overall population but significantly improved RFS in mrEMVI-positive patients.