Melatonin disruption negatively impacts breast cancer therapy

2014-10-01 11:03:38

A new study was published that examined circadian rhythms and breast cancer therapy ^[1]. Resistance to endocrine therapy (such as tamoxifen, a breast cancer drug) can be a major obstacle to successful treatment. Many forms of evidence link resistance to antiestrogen drugs in breast cancer cells with the overexpression or activation of pro-oncogenic tyrosine kinases. In addition, the disruption of circadian rhythms by night shift work or disturbed sleep-wake cycles may lead to an increased risk of breast cancer and other health conditions.

Light exposure at night suppresses the nocturnal production of melatonin (melatonin inhibits breast cancer growth). In this study, a rat model of estrogen receptor tumor were used to demonstrate how altering light and dark cycles with dim light exposure at night speed the development of breast tumours ^[1]. This speeds the development of breast tumours by increasing their metabolism and growth and conferring an intrinsic resistance to tamoxifen therapy. The authors identify that these characteristics were not observed in animals in which the circadian melatonin rhythm was not disrupted, or in animals subjected to dim light at night if they received nocturnal melatonin replacement. The results of the study also show that melatonin acts as a tumour metabolic inhibitor and a circadian-regulated kinase inhibitor that can re-establish the sensitivity of breast tumours to tamoxifen and tumour regression. The take-home message is that melatonin is extremely helpful and that disrupting the sleep-wake cycle can be harmful.