Abstract: The objective of this article is to review the basis supporting the usefulness of melatonin
as an adjuvant therapy for breast cancer (BC) prevention in several groups of individuals at high
risk for this disease. Melatonin, as a result of its antiestrogenic and antioxidant properties, as well
as its ability to improve the efficacy and reduce the side effects of conventional antiestrogens, could
safely be associated with the antiestrogenic drugs presently in use. In individuals at risk of BC due
to night shift work, the light-induced inhibition of melatonin secretion, with the consequent loss of
its antiestrogenic effects, would be countered by administering this neurohormone. BC risk from
exposure to metalloestrogens, such as cadmium, could be treated with melatonin supplements to
individuals at risk of BC due to exposure to this xenoestrogen. The BC risk related to obesity may be
reduced by melatonin which decrease body fat mass, inhibits the enhanced aromatase expression
in obese women, increases adiponectin secretion, counteracts the oncogenic effects of elevated
concentrations of leptin; and decreases blood glucose levels and insulin resistance. Despite compelling
experimental evidence of melatonin?s oncostatic actions being susceptible to lowering BC risk, there is
still a paucity of clinical trials focused on this subject.
