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Figure 1. Overview of key epigenetic mechanisms conferring drug resistance in breast cancer. This illustration highlights how epigenetic modifications significantly promote drug resistance in breast cancer. Breast cancer gene expression patterns are regulated by epigenetic changes such as DNA methylation and histone modification that remold chromatin structure and DNA accessibility. DNMT and DNA demethylase (TET: Ten-eleven translocation family proteins) are responsible for maintaining DNA methylation. Acetylation and methylation are the two fundamental ways that histones can be modified. Histone acetylation is controlled by HAT and HDAC, whereas histone methylation is regulated by histone demethylases and histone methyltransferases. The hypomethylation of oncogenes and the hypermethylation of tumor suppressor genes are important events that significantly impact drug responsiveness and the emergence of resistance by dynamically controlling the expression and functionality of genes essential for drug uptake, metabolism, and target interaction. Created in BioRender. Malhotra, D. (2025) oxxrw2s. DNMT: DNA methyltransferase; HAT: histone acetyltransferase; HDAC: histone deacetylase.