AFP and hepatocellular carcinoma: As a potential diagnostic biomarker for HCC, miR-21 has many unique advantages as compared with histopathological examination or AFP: (1) minimal invasiveness and convenience with no need of invasive or harmful procedures to obtained sample, (2) stability and reproducibility8 and early expression in HCC patients.31 In addition, as a marker for HCC, AFP level of 400 ng/ml is regarded as a threshold for screening of HCC patients.