Venous invasion detectable only by elastic stain shows weak prognostic value in colon cancer

Aims: Large venous invasion (VI) is prognostically significant in colon cancer. The increased use of elastic stains by pathologists results in higher VI detection rates compared to routine stains alone. This study assesses the prognostic value of VI detected by elastic versus routine stains.

Methods and results: Colon cancers resected between 2014 and 2017 underwent pathology slide review for VI. Cases without VI on routine stain were stained by elastic trichrome and re-examined. Demographic, clinical, pathological and outcome data were gathered by retrospective review. Kaplan-Meier curves with log-rank tests were performed for survival categorised by VI status. Cox regression was performed for multivariate analysis. Of 277 cases, 97 (35%) showed VI by routine stain alone, with an additional 58 (21%) discovered by subsequent elastic stains. Thus, elastic trichrome increased VI detection by 60%. However, only VI detected by routine stain showed worse overall survival (P < 0.001). VI detected by elastic stain only was not prognostically different from cases without VI (P = 0.428). For stage 2 cancers, VI was not prognostically significant regardless of method of detection. For stage 3 cases, only VI detected by routine stain was prognostic for overall survival (P = 0.002) with a hazard ratio of 4.04 by multivariate regression (P = 0.028).

Conclusions: VI detectable only by elastic stains do not show prognostic significance for survival in colon cancer. For pathologists with high baseline VI detections rates on routine stain, reflexive use of elastic stain may be of limited value.