Light Exposure May Increase Tamoxifen Resistance

the MPR take:

Exposure to even dim light at night may cause breast cancer tumors to become resistant to tamoxifen by suppressing melatonin production, a new study suggests. Researchers analyzed rats living in normal light and dark conditions (12 hours of light and 12 hours of complete darkness) or 12 hours of normal light and 12 hours of dim light. The tumors in the rats living in the dim light grew 2.6-fold faster vs. the tumors in the rats in the normal light and dark conditions. The tumors in the dim light group of rats were completely resistant to tamoxifen but regressed when the rats were given a nighttime melatonin supplement. The tumors in the normal light and dark conditions were significantly reduced with the tamoxifen sans melatonin. As tamoxifen resistance in patients with hormone receptor-positive breast cancer today remains an issue in cancer treatment, future research will likely examine a combination of melatonin and tamoxifen in individuals with breast cancer. Tamoxifen is an antiestrogen indicated for the treatment of metastatic breast cancer in men and women, axillary node-positive breast cancer in postmenopausal women after surgery and irradiation, axillary node-negative breast cancer in women after surgery and irradiation, reduction in risk of invasive breast cancer in women with ductal carcinoma in situ (DCIS) after surgery and radiation, and reduction in breast cancer incidence in high-risk women.

Light Exposure May Increase Tamoxifen Resistance
Light Exposure May Increase Tamoxifen Resistance

For rats bearing human breast tumors, exposure to dim light at night made the tumors resistant to the breast cancer drug tamoxifen, according to data published in Cancer Research, a journal of the American Association for Cancer Research. The negative effects of dim light exposure on tamoxifen treatment were overcome by giving rats a melatonin supplement during the night.

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