Melatonin, as most know, is the hormone most associated with sleep and the circadian rhythm. This hormone has displayed various positive benefits on the immune system as well.
As melatonin levels have been found to be low in those women suffering from endometrial cancer, its supplementation was investigated in this application.
When used together with estrogen therapy in animal models of menopause, melatonin supplementation demonstrated that the hormone significantly decreased endometrial cell proliferation and lower body weight in test animals. This study suggests that melatonin may be a useful compound as a cancer preventative.
Sources:
Effect of Melatonin on Intra-abdominal Fat in Correlation with Endometrial Proliferation in Ovariectomized Rats
The National Cancer Institute Office of Alternative and Complementary Medicine: Melatonin, Chronobiology and Cancer