PER1 and neoplasm: As shown in Figure 2D, compared with normal skin tissues, the expression of ARNTL, ARNTL2, CRY1, CRY2, CSNK1E, NR1D1, NR1D2, PER1, PER2, PER3, RORA, RORB, and RORC was significantly downregulated in tumor tissues (P<0.001), whereas the expression of CSNK1D and TIMELESS was significantly upregulated (P<0.001).