PER1 and hepatocellular carcinoma: Herein, we systematically characterized the expression pattern of core circadian clock genes, including ARNTL, CLOCK, CRY1, CRY2, DBP, NPAS2, NR1D1, NR1D2, PER1, PER2, PER3, RORA, and TIMELESS, and their clinical significances in HCC.