AIM: The expression pattern of endoglin (CD105) in hepatocellular carcinoma (HCC) has not been reported so far. We hypothesized that CD105 could differentially highlight a subset of microvessels in HCC, and intratumoral microvessel density (IMVD) by CD105 immunostaining (IMVD-CD105) could provide better prognostic information than IMVD by CD34 immunostaining (IMVD-CD34).METHODS: Paraffin blocks of tumor and adjacent nontumorous liver tissues from 86 patients who underwent curative resection of HCC were used for this study. Serial sections were stained for CD105 and CD34, respectively,to highlight the microvessels. IMVD was counted according to a standard protocol.RESULTS: In the HCC tissues, CD105 was either negatively or positively stained only in a subset of microvessels. In contrast, CD34 showed positive and more extensive microvessel staining in all cases examined. However, in the adjacent non-tumorous liver sections, CD105 showed a diffuse pattern of microvessel staining in 20 of 86 cases,while CD34 showed negative or only focal staining of the sinusoids around portal area. Correlation with clinicopathological data demonstrated that lower scores of IMVD-CD105 were found in larger sized tumors [mean 41.4/0.74 mm2 (＞5 cm tumor) vs 65.9/0.74 mm2(≤ 5 cm tumor), P = 0.043] and more aggressive tumors,as indicated by venous infiltration [36.8/0.74 mm2 (present)vs 64.2/0.74 mm2 (absent), P = 0.020], microsatellite nodules [35.1/0.74 mm2 (present) vs 65.9/0.74 mm2(absent), P = 0.012], and advanced TNM tumor stage [38.8/0.74 mm2 (stage 3 or 4) vs 68.3/0.74 mm2 (stage 1or 2), P = 0.014]. No prognostic significance was observed when median values were used as cut-off points using either IMVD-CD105 or IMVD-CD34. However, the presence of the diffuse pattern of CD105 expression in the adjacent non-tumorous liver tissues predicted a poorer disease-free survival (median 8.6 vs 21.5 mo, P = 0.026).CONCLUSION: Our data demonstrate that a lower IMVDCD105 is associated with larger and more aggressive tumors. In this study, IMVD-CD105 did not provide significant prognostic information. However, active angiogenesis as highlighted by diffuse CD105 staining of the microvessels in the adjacent non-tumorous liver tissues is predictive of early recurrence.