It is well known that hepatocellular carcinoma (HCC) commonly involves the local branches of portal and/or hepatic veins and causes a tumor thrombus even at a relatively early stage. Vascular invasion is classified as macrovascular invasion, which is grossly recognizable (mostly in large to medium vessels), or microvascular invasion (MVI), which can be identified only by microscopic observation (mainly in small vessels such as portal vein branches in portal tracts, central veins in noncancerous liver tissue, and venous vessels in the tumor capsule and/or noncapsular fibrous septa).
Although macroscopic vascular invasion in major vessels (and satellite nodules) is known to be a marker of poor outcomes after liver transplantation (LT) for HCC and is regarded as a contraindication for LT, the significance of MVI as a predictor of poor outcomes is still controversial. The controversy concerns the extent to which MVI (if it is identifiable before surgery) is a contraindication for LT, even though we know that only a minority of patients with MVI will experience HCC recurrence.
Methods
We searched the MEDLINE database (2002-2010) to determine the significance of MVI to the outcomes of LT for HCC; we used the keywords hepatocellular carcinoma, HCC, microvascular invasion, liver transplantation, and liver resection. We also performed a full manual search of the bibliographies of selected publications and included 4 additional publications from earlier years. Publications were included if they contained data on MVI and its relationship with tumor characteristics and/or prognostic data. The search resulted in a total of 48 relevant publications.
The publications were then ranked according to the classification proposed by the Oxford Centre for Evidenced-Based Medicine.
Results
Question 1. Is There Any Correlation Between MVI and Tumor Characteristics?
Many published studies have found that the presence of MVI is closely related to the tumor size, number, and histological grade 1-8 (Table 1). Esnaola et al. 1 studied MVI in 245 HCC patients who underwent surgical resection and fulfilled the Milan criteria, and they found that 33% of their patients had histopathological evidence of MVI. Patients with tumors larger