We've all heard of our biological clock. For some, it may tick at a fast clip while others' will tock at a more leisurely pace. Our biological clock drives circadian rhythms — physical, mental, and behavioral changes that follow a roughly 24-hour cycle.
Circadian rhythms respond primarily to light and darkness in an organism's environment. They are found in most living things, including animals, plants, and many tiny microbes. The study of circadian rhythms is called chronobiology — and now there is science behind the theory that targeting the biological clock could slow the progression of cancer.
According to a study conducted by Nicolas Cermakian, a professor in McGill University’s Department of Psychiatry, the results show for the first time that directly targeting the biological clock in a cancerous tumor has an impact on its development. Cermakian, who is also Director of the Laboratory of Molecular Chronobiology at the Douglas Mental Health University Institute, one of the research centers of the CIUSSS de l’Ouest-de-l’Île-de-Montréal. The findings were published in the journal BMC Biology. 
“Activating the biological clock in tumors could become an innovative approach in slowing their growth or that of metastases”, Cermakian said. “This would give people more time to use more conventional treatment modalities, such as surgery or chemotherapy. It now remains to be shown that we can target the clocks in human tumors the same way.”
Circadian clocks control cell cycle factors, and circadian disruption promotes cancer. To address whether enhancing circadian rhythmicity in tumor cells affects cell cycle progression and reduces proliferation, Cermakian's team compared growth and cell cycle events of B16 melanoma cells and tumors with either a functional or dysfunctional clock.
For this study, Silke Kiessling, a postdoctoral fellow on Cermakian's team, successfully adjusted the gears of the internal clocks in two types of cancer cells — skin and colon — to make them function properly. This repair, which was tested in mice and tissue cultures, slowed cancerous tumor growth. After about a week, the tumor treated in this manner was two-thirds smaller than the control tumor. 
“There were indications suggesting that the malfunctioning clock contributed to rapid tumor growth, but this had never been demonstrated,” Cermakian said. “Thanks to the use of a chemical or a thermic treatment, we succeeded in ‘repairing’ these cells’ clock and restoring it to its normal functioning. In these conditions, tumor growth drops nearly in half.”