The daily body clock gene Per1 may reduce cancer cell growth and tumor size at certain times of day

Breast cancer growth rate is gated by the circadian clock with two daily peaks and troughs.

• Cell cycle regulators, which control cell proliferation, show oscillating expression patterns linked to the circadian clock.
• Disruption of the circadian clock may lead to deregulated cell proliferation in cancer.
• The core clock gene Per2 is known to suppress cancer cell proliferation and tumor growth.
• Down-regulation of tumor Per1 is associated with increased cancer cell growth in vitro and tumor growth in vivo.
• Per1 appears to have a tumor-suppressor function that may reduce cancer proliferation at specific times of day.

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