Breast cancer patients who are hoping to slow down the rate that their tumors grow — which should be all of them — may soon find hope in the sleep hormone melatonin. A recent, early-stage study found that melatonin reduced tumor cell growth and the formation of new blood vessels by which they spread.

Although melatonin is mostly associated with our circadian rhythms and regulating sleep patterns, research has shown that it may play some role in slowing the spread of cancer. This could be, in part, because it’s considered to be a powerful antioxidant, which reduces the amount of cell-damaging free radicals in a person’s body, according to the American Cancer Society. To test its role in cancer treatment, researchers have used it alone and in combination with chemotherapy, radiation therapy, hormone therapy, and immunotherapy.

The current study looked at the effects of melatonin therapy with regard to tumor growth and angiogenesis, which is the formation of new blood vessels that help tumors spread, in mice with triple-negative breast cancer. The mice were administered pharmacological doses of melatonin one hour before the researchers turned the lights off, each night for 21 days — melatonin becomes most active in the dark. When the researchers looked at the cancer’s progression using single photon emission computed tomography, they found that the mice who underwent the therapy had smaller tumors and less vascular growth when compared to the control group. The findings were also replicated in cell models.

“These early stage research results with the melatonin drug in triple-negative breast cancer animal models achieved in our lab has not been seen anywhere else,” said Adarsh Shankar, co-author of the study and research assistant at the Department of Radiology at Henry Ford Hospital in Detroit, in a press release. “The key finding of the study is that we now know that we can trace this drug and its effect on tumor growth, which opens the door for more research on this topic.”          

Indeed, other research supports these findings. Just last month, two studies found a link between melatonin and cancer risk. One of them found that men who had higher levels of melatonin reduced their risk of prostate cancer by 75 percent. The other found that on-and-off patterns of sleep led to changes in the immune system that helped tumor growth become more aggressive. Obviously, there’s something promising in melatonin for cancer patients.

Affecting about one in eight women in the U.S., breast cancer only stands behind lung cancer as the most deadly among women, according to the National Institutes of Health. Although it also occurs in men, women are most at risk, and that risk increases as they age. The National Cancer Institute estimates that a woman’s risk increases from one in 227 to one in 42 as they go from age 30 to 50, respectively.

Source: Shankar A, Ali M, Arbab A, et al. Effect of Melatonin on Tumor Growth and Angiogenesis in Xenograft Model of Breast Cancer. PLOS One. 2014.