Circadian and melatonin disruption by exposure to light at night drives intrinsic resistance to tamoxifen therapy in breast cancer.
Level 5 - mechanism / opinion, no new human data
Preclinical animal model (rat xenograft study) without human clinical data.
PubMed 25062775 · doi:10.1158/0008-5472.CAN-13-3156
What was done
Researchers evaluated the effect of disrupted light/dark cycles using dim light exposure at night (dLEN) in a rat xenograft model bearing estrogen receptor-positive (ERα+) MCF-7 human breast cancer cells. They examined tumor development, metabolic activity, and response to tamoxifen therapy under normal light conditions, dLEN, and dLEN combined with nocturnal melatonin replacement therapy.
What was found
The abstract reports no numerical values, effect sizes, or statistical metrics. Qualitatively, dLEN accelerated breast tumor growth, enhanced tumor metabolism, and induced intrinsic resistance to tamoxifen. These effects were absent in rats with undisturbed circadian melatonin rhythms and were reversed in dLEN-exposed rats given nocturnal melatonin replacement, which restored tamoxifen sensitivity and induced tumor regression through tumor metabolic and kinase inhibition.
Why it matters
The study outlines a preclinical mechanism by which nighttime light exposure and circadian melatonin suppression impair the efficacy of standard endocrine therapy in ER-positive breast cancer. It suggests that maintaining circadian rhythms or providing timed melatonin supplementation could be relevant strategies to test in clinical endocrine resistance.
Limits
Findings are restricted to a rodent xenograft model using a single human cell line (MCF-7) and cannot be directly extrapolated to human patients. The abstract does not state sample sizes, light exposure parameters, drug or melatonin dosing, or quantitative outcome measures.
Cited by
- supports In breast cancer mouse models, nighttime light exposure makes tumors resistant to traditional chemotherapies, whereas complete darkness sensitizes them to treatment.