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Aim: Extramural venous invasion detected by MRI (mrEMVI) has in several expert centre studies been identified as an important prognostic factor in rectal cancer, and in guiding neoadjuvant therapy. However, population-based evidence for mrEMVI as a predictor for recurrent disease is lacking.

Method: This was a multicentre retrospective study based on the Swedish Colorectal Cancer Registry. The study period encompassed patients operated with abdominal resection for rectal cancer 2017–2021, with follow-up until January 2023. Patients diagnosed at hospitals with radiological registry data coverage <90% or with metastatic disease were excluded. Pretreatment mrEMVI constituted exposure, while recurrence-free survival was the main outcome. Distant and local recurrence, and overall survival were secondary outcomes, and pretreatment and postoperative scenarios were explored using multivariable Cox regression with multiple imputation. Hazard ratios (HRs) with 95% confidence intervals (CIs) were reported.

Results: A total of 2737 patients from 13 hospitals were eligible for analysis. Pretreatment mrEMVI was reported in 14.5% of patients, while 71.9% had negative findings and 13.6% had missing data. In the pretreatment scenario, mrEMVI was an independent predictor for worse recurrence-free survival with an adjusted HR of 1.64 (95% CI: 1.31–2.06). In the postoperative MDT setting, the influence of mrEMVI on recurrence-free survival decreased with an adjusted HR of 1.27 (95% CI: 1.00–1.61).

Conclusion: mrEMVI at diagnosis is an independent predictor of recurrence-free survival in an unselected population of rectal cancer patients undergoing abdominal resection.