PER1 and neoplasm: As summarized elsewhere [37], several core oscillator components act as tumor suppressors, and various tumors and tumor cell lines exhibit hyper- or altered methylation in the promoters of Per1, Per2, Per3, Cry1, Cry2 and Bmal1. These changes in the promoters may be regarded as a necessity for tumor cells to maintain their transformed state and to escape from circadian gating of the cell cycle.