Baseline characteristics of the studies in the meta-analysis.

Vascular invasion was defined as presence of either macro- or microscopic vascular invasion. Study quality was listed using the results of the Newcastle –Ottawa questionnaire. M, male; F, female; NR, not reported; OS, overall survival; DFS, disease-free survival; RT-PCR, reverse transcription-polymerase chain reaction; IHC, immunohistochemistry. ★2 represented more than 1% nuclear staining and/or with strong cytoplasmic staining. ▴The final score of each sample was assessed by the sum of the results of the intensity and extent of staining.