Prognostic value of the number and size of venous invasions in pT3 colorectal cancer: a prospective observational study.

Background: Although venous invasion is reportedly a clinically useful prognostic marker for colorectal cancer, suitable grading criteria have not been established.

Objective: This prospective observational study aimed to investigate the prognostic value of the number and size of venous invasions in patients with pT3 colorectal cancer.

Methods: We recruited 139 consecutive patients with pT3 colorectal carcinomas resected between October 2001 and August 2003. We used slides of whole-tissue sections stained with Elastica van Gieson. Venous invasion was classified according to the number of veins with carcinoma infiltration per slide with most venous invasions (V-number classification): V(n)-low 0-3 and V(n)-high ≥4. Additionally, the findings were classified according to the maximal size of veins containing carcinoma infiltration (V-size classification): V(s)-low <1 mm and V(s)-high ≥1 mm. The grades of venous invasions were evaluated just after surgery.

Results: The 5-year survival rate of V(n)-low and V(n)-high were 89.9 and 59.1 %, respectively (p < 0.0001). Comparisons between overall survival curves revealed that V-number classification (but not V-size classification) had a significant prognostic value in patients with pT3 cancer, especially in stage II patients (98.2 and 64.2 %, respectively; p < 0.0001). Multivariate analysis revealed distant metastasis, age, and V-number classification (hazard ratio 3.1; p = 0.0071) as independent prognostic indicators.

Conclusions: V-number classification may be a useful prognostic system when evaluating and sub-grouping patients with pT3 colorectal cancer.