Night-time dim-light exposure could make breast cancer spread to bone

Breast cancer patients, who expose themselves to dim-light at night, take note! A recent study has found out that dim-light exposure at night could likely lead breast cancer to spread to bone.

Study presented at Endocrine Society's annual meeting, ENDO 2019, has shown dim-light exposure at night may lead breast cancer to spread to bone for the first time in an animal study.

"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," said Anbalagan.

"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." said Muralidharan Anbalagan, Ph.D., assistant professor, Tulane University School of Medicine in New Orlean.

More than 150,000 U.S. women had breast cancer in 2017 that metastasised, or spread outside the breast, according to an estimate from the National Cancer Institute. When breast cancer spreads, it often goes to the bones, where it can cause severe pain and fragile bones.

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 strong night-time circadian melatonin signal. This night-time melatonin signal has been shown to produce strong anti-cancer actions and also promotes sleep.

All mice were kept in the light for 12 hours each day. One group of three mice was in the dark the other 12 hours, which helped them produce high levels of endogenous melatonin. Another group spent 12 hours in light followed by 12 hours in dim light at night, which suppresses their nocturnal melatonin production. The dim light was 0.2 lux, which is less than a night-light or a display light from a cell phone, according to Anbalagan.

X-ray images showed that mice exposed to a light/dim light cycle had much larger tumors and increased bone damage compared with mice kept in a standard light/dark cycle, he reported.

"Our research identified the importance of an intact nocturnal circadian melatonin anti-cancer signal in suppressing bone-metastatic breast tumour growth," Anbalagan said.

The ultimate goal of their research, he said, is to find a way to inhibit or suppress the progression of breast cancer metastases to bone.