Melatonin is a hormone that communicates information concerning environmental light conditions to various parts of the body and plays a vital role in the synchronization of circadian rhythms. It is synthesized and secreted by the pineal gland in the brain. Decreased melatonin production has been linked to increased breast cancer risk. Habitually sleeping in the presence of artificial light appears to heighten breast cancer risk by inhibiting melatonin production. While most studies have focused on melatonin's chemopreventive activities in hormone receptor positive (ER+/PR+) breast cancer cells, there is some evidence that melatonin can also have beneficial effects in hormone receptor negative (ER-/PR-) disease. Now a new study has reported that melatonin treatment showed effectiveness in reducing tumor growth, cell proliferation, and angiogenesis in an animal model of triple negative (ER-/PR-/HER2-) breast cancer.

Anti-cancer activities of melatonin

Melatonin influences the expression of genes involved in cell proliferation, immune responses, cell adhesion, apoptosis (programmed cell death), cell cycle, and angiogenesis (new blood vessel formation) in ways that have anticancer effects in breast cancer cells. For example, melatonin induces the expression of tumor suppressor genes. Melatonin has also been shown to interfere with estrogen-signaling pathways and reduce aromatase activity (in which androgens are converted into estrogens) in human breast cancer cells, thereby inhibiting ER+ breast cancer growth.

Latest research finds melatonin reduces growth, proliferation, and angiogenesis

The study referenced at the beginning of this news story was designed to investigate the effects of melatonin on angiogenesis in an animal model of triple negative breast cancer. To conduct the study, the authors implanted triple-negative breast cancer cells (MDA-MB-231) in mice. The mice were treated with melatonin for 21 days, using intraperitoneal (body cavity) injections one hour before turning off the room light. A group of control mice did not receive melatonin. The volume of tumors in the mice was measured weekly with a digital caliper. At the close of the study, the tumors were analyzed to evaluate expression of pro-angiogenic/growth factors and angiogenesis.

Melatonin-treated mice were found to have smaller tumor size and lower cell proliferation (measured by Ki-67) than control animals. Expression of VEGF (vascular endothelial growth factor), a key molecule in promoting angiogenesis) receptor 2 was significantly lower in treated animals compared to controls when determined by immunohistochemistry but the changes were not significant on SPECT (single-photon emission computed tomography) images. The authors also observed a decrease of micro-vessel density in melatonin-treated animals. On the other hand, there was some evidence of increased expression of EGFR (epidermal growth factor receptor) and IGF-1 (insulin-like growth factor 1) in treated tumors. The authors conclude that melatonin treatment showed effectiveness in reducing tumor growth, cell proliferation, and angiogenesis in this animal model of breast cancer.

Please see our article on what triple negative patients and survivors should eat for more information.