The pineal gland and breast cancer: serum levels of melatonin in patients with mammary tumors and their relation to clinical characteristics

Several studies have suggested that the pineal gland hormone melatonin may influence the growth of breast cancer. The importance of melatonin blood concentrations in the clinical history of human breast cancer, however, has still to be defined. To further investigate this problem, we used a RIA method to assay serum levels of the pineal hormone in 74 untreated breast cancer patients, clinical stage T1-3 NO-2 MO, and in 46 age-matched healthy women as controls. Mean serum melatonin levels were significantly higher in patients than in controls. Melatonin concentrations were highest in breast cancer patients with the best prognosis (i.e. estrogen receptor-positive/node-negative cases). Mean levels of melatonin were significantly higher in estrogen receptor-positive patients than in the negative ones. They were also higher in node-negative than in node-positive cases, and in progesterone receptor-positive patients than negative ones, but none of these differences was statistically significant. No difference was observed in relation to menopausal status and to tumor histotype. These results suggest that melatonin plays a role in the hormone-dependency of human breast cancer.