PTEN and hepatocellular carcinoma: Recent studies have shown that overexpression of miR-21 could increase the methylation level of the phosphatase and tensin homolog pseudogene 1 (PTENp1) promoter by regulating ten eleven translocation (TET) expression, thereby inhibiting PTENp1 expression, thus leading to downregulation of PTEN and affecting the growth of HCC cells (Cao et al., 2019).