PER1 and cancer: In general, various genes, including CLOCK, ARNTL, PER1/2/3, and CRY1/2, form the core components of the mammalian circadian clock (CCMCCs), and these establish complicated molecular circuits that orchestrate the different phases of the circadian rhythm.20, 21 Furthermore, the expression of a substantial fraction (~5%‐20%) of genes is under the control of the circadian rhythm.20, 21 According to the Circadian Gene Database (CGDB),23 nearly 2000 genes show rhythmic expression, and many of these have been implicated to play roles in cancer.