The Role of Melatonin in Breast Cancer

Abstract

Abstract Melatonin is a hormone secreted by the pineal gland, responsible for the regulation of the circadian rhythm. Beyond its primary function, it has been implicated in various physiological processes and research suggests a potential link between melatonin and malignancy and particularly breast cancer. The aim of this thesis was to investigate the role of melatonin in breast cancer. Paper I examined the association between melatonin intake and survival in postmenopausal women diagnosed with early breast cancer, assessing the possible protective role of melatonin on survival. While melatonin consumption was associated with improved breast cancer-specific survival in univariable analysis, the effect was no longer significant after adjusting for known predictive and prognostic variables. Paper II investigated the expression of MT1 melatonin receptor in luminal invasive ductal breast carcinoma in postmenopausal women, in relation to prognostic and predictive factors and survival. No significant associations were observed between MT1 receptor expression and either clinicopathological parameters or survival. Paper III assessed cancer risk in visually impaired individuals and their matched controls. Visual impairment was associated with increased risk for cancer overall, and for specific types including breast. Various confounding factors could explain this association. Paper IV evaluated the addition of melatonin to systemic oncologic treatment of patients with metastatic breast cancer, in relation to tumor response and survival. The analysis revealed significantly improved tumor response rates and 1-year survival among patients receiving melatonin in combination with standard therapy. In conclusion, melatonin was not found to have a significant effect on the survival of patients with early breast cancer. MT1 receptor expression was not correlated with prognostic or predictive factors or survival. Visual impairment was associated with increased cancer risk overall and for specific cancers. The addition of melatonin to standard treatment in patients with stage IV breast cancer showed enhanced tumor response and improved survival.