Dim Light at Night May Help Spread Breast Cancer to Bones

When breast cancer spreads, it often goes to the bones, and new research has found that exposure to dim light at night may contributor to this spread. Results from the animal study were presented at ENDO 2019, the annual meeting of the Endocrine Society.

Breast cancer that has spread to the bones is a major source of morbidity and mortality. Cancer that has been spread to the bone can cause severe pain and fragile bones, and it cannot be surgically removed—it can only be treated with chemotherapy and/or radiation.

The researchers injected estrogen receptor-positive human breast cancer cells into the shinbone of female mice who had a strong nighttime circadian melatonin signal. The mice were kept in the light for 12 hours. One group of mice was in the dark for the remaining 12 hours, while another group spent the remaining 12 hours in dim light, which suppresses nocturnal melatonin production.

These mice in the dim light developed full blown breast cancer tumors in bone (P <.05) that are highly osteolytic (P <.05).

"To date, no one has reported that exposure to dim light at night induces circadian disruption, which then increases the formation of bone metastatic breast cancer,” Muralidharan Anbalagan, PhD, assistant professor, Tulane University School of Medicine, said in a statement. “This is important, as many patients with breast cancer are likely exposed to light at night as a result of lack of sleep, stress, excess light in the bedroom from mobile devices and other sources, or night shift work.”

The researchers shown that chronotherapeutic use of doxorubicin (Dox) in circadian alignment with melatonin reduced tumor growth and bone erosion.

“Successful use of this chronotherapeutic use of Dox and [melatonin] in clinical trials increasing efficacy in preventing or suppressing breast cancer metastasis to bone while decreasing toxic side effects of doxorubicin would provide a revolutionary advancement in the treatment of bone metastatic breast cancer and decrease the morbidity and mortality associated with breast cancer metastasis to bone,” the authors concluded.

Reference

Anbalagan M, Dauchy RT, Xiang S, et al. Disruption of the circadian melatonin signal by dim light at night promotes bone-lytic breast cancer metastases. Presented at: ENDO 2019; March 23-26, 2019; New Orleans, Louisiana.