PER1 and breast cancer: Moreover, the recent GWAS study conducted by Mocellin et al. has shown a highly significant association between the breast cancer risk and circadian pathway variation (p-value 1.9 × 10−6) The top genes and number of SNPs involved in cancer development were RORA and RORB (eight SNPs and five SNPs, respectively); other significant genes with single SNPs were PER1 (two SNPs), ARNTL, CRY2, CLOCK, CRY1, and RORC, in order of significance.