Breast cancer risk, epigenetic aging and DNA methylation clocks

Breast cancer is the most frequently diagnosed cancer and the second leading cause of cancer death among women in the United States, and is globally a common and impactful cancer. Its distinct molecular subtypes, each defined by characteristic genomic and epigenomic profiles, vary substantially in initiation risk, progression, and therapeutic outcome. Chronological age is a risk factor for all cancers, but biological age, which reflects the cumulative impact of environmental and lifestyle exposures on physiological systems, has emerged as a framework for explaining this risk and outcome heterogeneity. Epigenetic age offers a measurable proxy for biological age, captured through epigenetic clocks that integrate DNA methylation (DNAm) patterns across the genome. Integrating DNAm-based epigenetic age with transcriptomic and proteomic data from individuals at diagnosis or elevated risk offers a route to predictive tools for personalized risk stratification, prevention, and survivorship care. We examine the development and biological basis of DNAm epigenetic clocks and their emerging role in breast cancer risk, tumor biology, and clinical outcomes. Established risk factors including estrogen exposure, menopause, elevated body mass index (BMI), and mammographic breast density accelerate epigenetic aging, suggesting that clocks encode cancer risk information beyond that captured by chronological age alone. We discuss epigenetic age as a biomarker for early detection, risk stratification, and therapeutic intervention, highlighting its promise for precision oncology and personalized prevention, treatment, and survivorship care. We also consider the unique epigenetic dynamics of pregnancy, which induces transient age acceleration followed by a potential postpartum reversal, and evaluate the translational potential of circulating cell-free DNA (cfDNA) fragmentomics and epidrugs, including DNA methyltransferase (DNMT) and histone deacetylase (HDAC) inhibitors, for early detection and therapeutic intervention. Epigenetic clocks represent a potentially transformative tool for breast cancer risk stratification and precision oncology. Integrating DNAm-based biological age with multi-omic data offers a pathway toward personalized care and real-time monitoring of therapeutic response, including guiding screening intensity for high-risk individuals and serving as dynamic monitors of preventive or survivorship interventions. Future research must prioritize longitudinal studies and ancestral diversity to establish causality and ensure clinical utility across all patient populations.