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Background
Hepatocellular carcinoma (HCC), the major primary liver cancer, is the sixth most common malignancy in the world [1]. This malignancy is aggressive and the prognosis is poor if the tumors are found at a late stage [2, 3]. Even if the tumors are found at an earlier stage and removed totally by liver resection or liver transplantation, the treatment results are still not satisfactory because the tumors are easy to recur [4, 5]. In liver resection, tumor recurrent rate is as high as 65% within 3 years [4]. In liver transplantation, the tumors may recur in a small proportion of patients even if the tumors are within Milan criteria [6, 7]. If liver transplantation is performed for an advanced HCC, tumor recurrence is a predestination although native liver was removed and a new liver was implanted [8]. Undoubtedly, tumor recurrence remains a critical and unsolved issue which interferes with a successful treatment for HCC no matter liver resection or liver transplantation is performed.
Many prognostic factors are related to tumor recurrence after liver resection or liver transplantation [9, 10]. By biostatistics analysis, vascular invasion is always one of the most important risk factors of tumor recurrence either in liver resection or liver transplantation [4, 11, 12]. Why HCC facilitates to grow into portal venules is still a mystery. The only thing known is that the incidence of vascular invasion for HCC increases when the tumor size becomes large [13]. The Liver Cancer Study Group of Japan reported that the incidence of portal vein thrombosis (PVT) was 62% in autopsy [14]. Portal vein thrombosis is an extreme form of vascular invasion for HCC. Once upon PVT is noted, intrahepatic metastasis and distal metastasis are intended to occur. Portal vein thrombosis has been described as one of the three independent factors to predict shorter survival for untreated HCC [15]. In another study, PVT was also mentioned as one of the most robust predictors to predict death [16]. The life span for the patients having PVT in 1st or 2nd branches of portal veins is only 4-6 months. If PVT approaches to main portal vein, all treatments are not effective and the life span is reduced to 2-3 months only [17]. Thus, it is essential to understand...