Survival outcomes of different neoadjuvant treatment regimens in patients with locally advanced rectal cancer and MRI‐detected extramural venous invasion

PURPOSE: MRI‐detected extramural venous invasion (mrEMVI) is associated with poor survival outcomes in patients with locally advanced rectal cancer (LARC). An mrEMVI‐positive status is considered a strong indication for neoadjuvant treatment, but the optimal regimen is unknown. PATIENTS AND METHODS: We retrospectively compared pathological and survival outcomes of 584 patients diagnosed with mrEMVI‐positive rectal cancer between January 2013 and October 2021, and receiving either neoadjuvant chemotherapy (NCT) alone, neoadjuvant chemoradiotherapy (nCRT) alone, or nCRT plus NCT, prior to total mesorectal excision. Propensity score matching (PSM) was used to balance clinical bias between groups, which were compared using chi‐square testing and Kaplan–Meier curves. RESULTS: Median follow‐up was 33.9 (range, 10.2–100.4) months. The 3‐year overall survival (OS), disease‐free survival (DFS), distant metastasis‐free survival (DMFS), and locoregional relapse‐free survival (LRFS) rates for all patients were 90.4%, 57.5%, 61.1%, and 85.7%, respectively. Of 584 mrEMVI‐positive patients at the time of diagnosis, 457 (78.3%) were EMVI‐negative on surgical pathology, and they had significantly better 3‐year OS, DMFS, DFS, and LRFS rates (all p < 0.001) than patients who remained EMVI‐positive. After PSM was applied, patients receiving nCRT alone had significantly better 3‐year OS (96.8% vs. 86.5%, p = 0.005) and DMFS (67.1% vs. 53.5%, p = 0.03) rates than those receiving NCT alone. Patients receiving NCT plus nCRT had higher pathological complete response (PCR) (10.8% vs. 2.7%, p = 0.04) and downstaging (33.8% vs. 5.3%, p < 0.001) rates than those receiving nCRT alone, but survival rates did not differ (all p > 0.05). CONCLUSION: Most EMVI‐positive patients with LARC converted to EMVI‐negative after neoadjuvant treatment, resulting in improved OS and DFS. Patients receiving nCRT had more favorable survival outcomes than those receiving NCT, suggesting the importance of including neoadjuvant radiotherapy. Patients receiving NCT in addition to nCRT had higher rates of PCR and downstaging, but their survival rates were not better.