These epidemiological studies are supported by GWAS analyses that have revealed a significant statistical association between genetic variation located in circadian genes (ARNTL, CLOCK, CRY1, CRY2, RORA, RORB, RORC, PER1) and the risk of breast cancer, as well as between circadian clock-gene expression and metastasis-free survival7,8. This evidence concerns the gene CLOCK and breast carcinoma.