Early Menarche and Breast Cancer Risk: A Systematic Review

Abstract

Objective: To evaluate the association between early menarche and breast cancer risk, including incidence, tumor characteristics, and hormonal mechanisms. Methods: A systematic review was conducted using PubMed and Google Scholar to identify relevant peer-reviewed cohort, case-control, and longitudinal studies examining pubertal timing and breast cancer outcomes. Early menarche was defined as occurring before age 12. Extracted data included relative risk (RR), odds ratios (OR), hazard ratios (HR), confidence intervals (CI), and p-values. Results: Several studies demonstrated that early menarche is associated with an increased risk of breast cancer, particularly estrogen receptor–positive tumors. Early menarche was also linked to prolonged estrogen exposure, lower levels of sex hormone-binding globulin (SHBG), a protein that regulates the availability of sex hormones in circulation, and increased breast density. Conclusions:Early menarche is a significant risk factor associated with increased breast cancer incidence and tumor characteristics.