HCC in the major bile duct, especially in the common bile duct, can cause obstructive jaundice . Such HCCs are called icteric-type HCCs and tend to be complicated by advanced clinical stage . The most typical clinical finding is obstructive jaundice confused with cholangiocarcinoma . Although most cases seem to originate from tumor thrombi, the thrombi rarely stick to or invade the bile duct wall [3, 4]. This case is unique because the recurrent HCC tumor due to hematogenous metastasis penetrated the bile duct wall and generated a tumor thrombus 50 months after the initial surgery. To the best of our knowledge, except for our case, there has been only one report of hematogenous HCC recurrence in the bile duct . However, their diagnosis was based only on circumstantial evidences, i.e., clinical and microscopic. Besides HCC, there are three cases of colon [6, 7], two of kidney [8, 9], and one of lung  cancers that reportedly showed metastasis to the common bile duct. All the cases were strongly considered that hematogenous metastasis from the viewpoint of the anatomical positional relationship between the common bile duct and each organ.
There are some rare reports of extrahepatic HCC without primary hepatic parenchymal lesions [2, 11]; hence, the bile duct tumors in this case might be new HCC lesions. However, the bile duct tumors in this case were considered recurrence because of the morphological similarities and venous invasion. Furthermore, most cases of primary extrahepatic HCC are continuous and localized masses , whereas the tumors in this case are extensively distinct and scattered.
HCC recurrence can be explained by the following points: (i) invasive recurrence from microscopic bile duct invasion; (ii) infiltrating recurrence of tumor thrombus having been incompletely removed during primary hepatectomy; (iii) invasion from the surrounding tissues of the common bile duct; or (iv) recurrence of hematogenous metastasis with microscopic venous invasion. In this case, no microscopic bile duct invasions were observed in the primary or recurrent HCCs. Furthermore, most recurrences originating from tumor thrombus have been reported to develop within a year of surgery , unlike this case in which recurrence occurred 50 months after primary hepatectomy. Although a polypoid tumor was observed to break through a part of the epithelium, numerous lesions were extensively observed subepithelially. Therefore, we consider that the recurrence originated from hematogenous metastasis with microscopic venous invasion, and the tumor thrombus was separated from the polypoid tumor.
In this case, because (a) there were severe portal invasion, (b) tumor thrombus was located in the left portal vein, and (c) there were several daughter nodules of microscopic intrahepatic metastasis, the patient had high chance of recurrence. Despite such high-risk histopathological findings, it is very interesting that he had a disease-free interval of 50 months before recurrence.
The effectiveness of surgery for recurrence originating from tumor thrombus has been previously reported [13, 14]. Although thrombectomy is effective in the treatment of bile duct tumor thrombus, positive outcomes of bile duct resection with thrombus have been reported when tumor thrombus has invaded the bile duct epithelium. However, the recurrence in this case originated from hematogenous metastasis and exhibited aggressive behavior after the bile duct resection. Therefore, further cases and studies are needed to reveal the effectiveness of surgery.