Developments in the assessment of venous invasion in colorectal cancer: implications for future practice and patient outcome.

Venous invasion, or "large vessel" invasion, is a known independent prognostic indicator of distant recurrence and survival in colorectal cancer. Accurate assessment of venous invasion is of particular importance in stage II disease because it may influence the decision to administer adjuvant therapy. Venous invasion is widely believed to be an underreported finding with significant variability in its reported incidence. In the most recent College of American Pathologists' cancer reporting protocol, venous invasion is not recorded separately from lymphovascular, or "small vessel" invasion, which may not be appropriate because these features confer differing prognostic information. The presence of extramural venous invasion is strongly predictive of adverse outcome, although the prognostic significance of intramural venous invasion remains unknown. There are no formal guidelines regarding the pathologic assessment of venous invasion or the application of specific reporting criteria. The routine use of an elastic stain results in an almost 3-fold increase in the venous invasion detection rate when compared with a standard hematoxylin and eosin stain and may be a cost-effective means of increasing the diagnostic yield of venous invasion. The development of high-resolution magnetic resonance imaging, where extramural venous invasion can be detected preoperatively, may also influence the manner in which pathologists process specimens. This review focuses on recent developments in the assessment of venous invasion and highlights their potential impact on future practice.