ACTB and cancer: The cfDII of other repeat elements LINE-1 and housekeeping genes such as β-actin and GAPDH are also explored as liquid biopsy marker in different cancers including HCC (Chen et al., 2012), pancreatic cancer (Tuchalska-Czuron et al., 2020), breast cancer (Cheng et al., 2018), and renal cell carcinoma (Gang et al., 2010).