The Menstrual Cycle Related Hormone Variations and Breast Cancer Risk: A Novel Theory

Abstract

Background: The cumulative and excessive exposures to estrogen contributing to increased risk of breast cancer may be misleading. Methods: We proposed a novel theory to highlight that exposure to unstable estrogen levels may play a critical role in determining breast cancer risk among females as the change of endocrine environment may pose a risky environment to breast tissues for carcinogenesis. Particularly, we considered the menstrual cycle related estrogen variation (MCREV) as the primary hazard to breast cancer among females. Results: To describe MCREV, its intensity was defined as the difference between the highest and the lowest levels of estrogen within a menstrual cycle; its timing was defined as age at menarche and age at pregnancies (i.e. timing of cessation of exposure to this hazard); and its frequency and duration can both be defined as the total number of menstrual cycles, which is influenced by many factors including age of menarche, age of menopause, average length of one menstrual cycle, and durations and number of pregnancies and breastfeeding. Conclusions: The proposed MCREV theory may identify women at high-risk of breast cancer at an earlier age. The development of breast cancer might be weakened if suitable techniques to reduce the MCREV become clinically available. This novel theory opens a new door in breast cancer prevention and management.