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Study Reveals Dim Light at Night May Promote Breast Cancer Metastasis to Bone

A researcher poses in his lab.

While insufficient sleep has been shown to have a litany of adverse endocrine effects, a new study presented at the Endocrine Society's recent 2019 Annual Meeting here in New Orleans revealed the possible dangers of dim light exposure at night that could cause breast cancer to metastasize to the bones.

Muralidharan Anbalagan, PhD , assistant professor of structural and cellular biology, showed for the first time in a mouse study that exposure to artificial dim light at night may contribute to the spread of breast cancer to the bones.

Results of the study were presented at ENDO 2019, the Endocrine Society's recent annual meeting in New Orleans, and were featured in the April issue of the Endocrine News ( Pillow Talk by Derek Bagley ).

"To date, this is the first report that circadian disruption, via exposure to artificial dim light at night-induced suppression of nighttime melatonin production, increases the formation of bone metastatic breast cancer," said Anbalagan. "This is important, as many patients with breast cancer are likely to be exposed to light at night as a result of lack of sleep; stress; night shift work; and excess light in the bedroom from mobile phones, iPads, laptops, televisions, night lights, and even street lights."

According to the National Cancer Institute, more than 150,000 American women had breast cancer that metastasized, or spread outside the breast, in 2017. When breast cancer spreads, it often goes to the bones, where it can cause severe pain and fragility.

In this preliminary study funded by the Louisiana Clinical and Translational Science Center (LACATS) in collaboration with the Louisiana Cancer Research Center (LCRC) and the Tulane Center for Circadian Biology, the researchers created a mouse model of bone metastatic breast cancer.

They injected estrogen receptor-positive human breast cancer cells that have a low propensity to grow in bones into the tibia, or shinbone, of female mice. Like humans, the mice used in this study produce a robust nighttime circadian melatonin signal. This nighttime melatonin signal has been shown to produce strong anti-cancer actions and also promote sleep.

All mice were kept in bright light for 12 hours each day. One group of three mice was in complete darkness the other 12 hours, which allowed them to produce high levels of endogenous melatonin at night. Another group spent 12 hours in bright light followed by 12 hours in dim light at night - less that that produced by a night light or cell phone display - which suppressed their nocturnal melatonin production.

IVIS small animal images and x-ray images showed that mice exposed to a bright light/dim light cycle had much larger tumors and increased bone damage compared with mice kept in a standard bright light/complete dark cycle.

"For the first time, our research demonstrated that dim light at night suppression of the circadian nighttime melatonin signal stimulated breast cancer bone metastasis. At the same time, our study identified the importance of an intact nocturnal circadian melatonin anti-cancer signal in suppressing bone-metastatic breast tumor growth," said Anbalagan.

The ultimate goal of this research, according to Anbalagan, is to reveal the key players involved in promoting breast cancer growth in bone and the involvement of melatonin receptors. In the meantime, he reminds everyone that the circadian system is extremely important for overall health. "Circadian disruption by light at night is not only a risk factor in cancer, but also in other metabolic diseases," he says. 

This content was originally posted by Tulane University.