LAUSR

Extramural venous invasion (EMVI) is a well‐known prognostic factor in colorectal cancer (CRC). Vascular invasion within the bowel wall, intramural vascular invasion (IMVI), has received less attention and its incidence and prognostic importance in CRC is not completely known. A systematic literature search was performed focusing on the impact of IMVI in CRC. Data were analysed using Review Manager version 5.3 on incidence and clinical endpoints local recurrence, 5‐year cancer‐specific survival (CSS) and 5‐year overall survival (OS). Meta‐analysis was performed in terms of risk ratios (RR) and hazard ratios (HR) with 95% confidence interval (95% CI). Of the initial 1199 papers identified by our search strategy, 20 were included in this meta‐analysis. Of the 8078 included patients, 1008 patients had IMVI (12.5%). Studies that re‐examined histological slides showed a higher incidence of IMVI compared to studies extracting IMVI from pathology reports (17.6 versus 7.7%, P < 0.001). Detection of IMVI increased significantly with the use of additional staining (22.9 versus 12.3%, P < 0.001). IMVI was associated with a decreased CSS HR: 1.6, 95% CI 1.2–2.2 in multivariate analysis). A borderline significant effect was observed for IMVI on local recurrence (RR: 1.5, 95% CI: 0.98–2.3) and OS (RR: 1.2, 95% CI: 1.0–1.4). In conclusion, despite the limited number of studies, there is a clear association with outcome in the presence of IMVI. This warrants more attention to this under‐reported prognostic factor.