Moreover, knockdown of circ_0015756 could inhibit tumor metastasis and invasion through miR-610/FGFR1; Yang et al. [73] reported that has_circ_0039053 could accelerate proliferation and invasion via the miR-637/USP21 axis in HCC cells; and Wu et al. [74] found circRASGRF2’s function as an oncogenic agent in HCC, and knockdown of circRASGRF2 suppressed the proliferation and migration of HCC cells by upregulating FAK expression through sponging miR-1224. Here, USP21 is linked to hepatocellular carcinoma.