The prognostic significance of postchemoradiotherapy high-resolution MRI and histopathology detected extramural venous invasion in rectal cancer.

Objective: This study aimed to determine the prognostic significance of extramural venous invasion (EMVI) after chemoradiotherapy (CRT) by both magnetic resonance imaging (MRI) (ymrEMVI) and histopathology (ypEMVI).

Background: EMVI is a prognostic factor in rectal cancer but whether this remains so after CRT preoperative is unknown. Histopathological definitions of EMVI are variable and lead to underreporting particularly after CRT.

Methods: All consecutive patients staged on initial MRI as EMVI-positive undergoing preoperative CRT and curative surgery between Jan 2006 and Jan 2012 were included. Posttreatment EMVI status (yEMVI) was reevaluated for both MRI and pathology. The primary endpoint of disease-free survival (DFS) for ymrEMVI and ypEMVI was calculated using the Kaplan-Meier product limit and compared with a Mantel-Cox log-rank test. A P < 0.05 was considered significant. Hazard ratios (HRs) for disease recurrence were generated using Cox proportional hazard regression for MRI and histopathology tumor characteristics.

Results: A total of 188 patients who had evidence of EMVI on initial baseline MRI staging were included. MRI detected significantly more patients with persistent EMVI than histopathology (53% vs 19%) but both were prognostic for worse survival-ymrEMVI (HR 1.97) and ypEMVI (HR 2.39). Patients with persistent ymrEMVI-positivity had significantly worse DFS at 3 years (42.7%) compared with ymrEMVI-negative tumors (79.8%); DFS for was 36.9% versus 65.9% positive and negative ypEMVI, respectively.

Conclusions: Detection of EMVI post-CRT is prognostically significant whether detected by MRI or histopathology. EMVI status after treatment may be used to counsel patients regarding ongoing risks of metastatic disease, implications for surveillance, and systemic chemotherapy.