Similarly, downregulation or upregulation of Per1, Per2, and Cry1, the principal target genes of BMAL1/CLOCK, has been shown to promote or suppress tumor incidence and proliferation, respectively, in multiple cancer cell types, including Lewis lung carcinoma and mammary carcinoma cells34, pancreatic cancer35, lung carcinoma4, leukemia36,37, glioma38, ovarian cancer39, and oral squamous cell carcinoma40,41. Here, PER2 is linked to breast carcinoma.