A systematic review of microvascular invasion in hepatocellular carcinoma: diagnostic and prognostic variability

Selected patients with hepatocellular carcinoma are candidates to receive potentially curative treatments, such as hepatic resection or liver transplantation, but nevertheless there is a high risk of tumor recurrence. Microvascular invasion is a histological feature of hepatocellular carcinoma related to aggressive biological behavior. We systematically reviewed 20 observational studies that addressed the prognostic impact of microvascular invasion, either after liver transplantation or resection. Outcomes were disease-free survival and overall survival. In liver transplantation, the presence of microvascular invasion shortened disease-free survival at 3 years (relative risk (RR)=3.41 [2.05-5.7]; five studies, n=651) and overall survival both at 3 years (RR=2.41 [1.72-3.37]; five studies, n=1,938) and 5 years (RR=2.29 [1.85-2.83]; six studies, n=2,003). After liver resection, microvascular invasion impacted disease-free survival at 3 and 5 years (RR=1.82 [1.61-2.07] and RR=1.51 [1.29-1.77]; four studies, n=1,501 for both comparisons). However inter/intraobserver variability in reporting and the lack of definition and grading of microvascular invasion has led to great heterogeneity in evaluating this histological feature in hepatocellular carcinoma. Thus, there is an urgent need to clarify this issue, because determining prognosis and response to therapy have become important in the current management of hepatocellular carcinoma. In this systematic review, we summarize the diagnostic and prognostic data concerning microvascular invasion in hepatocellular carcinoma and present a basis for consensus on its definition.