Curcumin and Cancer Stem Cells: Epigenetic Mechanisms Underlying Therapeutic Resistance and Tumor Relapse.

Cancer stem cells (CSCs) drive therapeutic resistance, metastasis, and tumor recurrence through reversible transitions among stem-like, differentiated, epithelial, and mesenchymal states, which are sustained by interconnected epigenetic mechanisms. To our knowledge, this is the first review to integrate curcumin-mediated regulation of DNA methylation, chromatin remodeling, and non-coding RNAs within a single CSC plasticity framework and to propose the concept of an "epigenetic collapse of CSC plasticity" as a mechanistic explanation for how curcumin may weaken stemness, state switching, and adaptive treatment resistance. Evidence was critically evaluated through structured searches of PubMed/MEDLINE, Scopus, Web of Science Core Collection, Google Scholar, and citation tracking, while direct curcumin-epigenetic evidence was distinguished from independent CSC evidence and inferential mechanistic links. Curcumin has been reported to modulate DNMT1 and locus-specific DNA methylation; regulate HDACs, p300/CBP, EZH2, H3K27me3, and BMI1; and alter selected microRNA, long non-coding RNA, and circular RNA pathways, with comparatively stronger evidence involving the miR-34 family, miR-200c, miR-21, H19, and circHN1. However, current evidence is constrained by the predominance of bulk cancer-cell models, heterogeneous formulations and exposure conditions, and the scarcity of epigenetic rescue experiments combined with rigorous functional CSC assays. By unifying previously fragmented epigenetic evidence, this review advances a new evidence-weighted model in which curcumin may suppress CSC persistence not through a single molecular target, but by destabilizing the multilayer epigenetic circuitry that enables plasticity. Curcumin should therefore be regarded as a context-dependent, multilayer epigenetic modulator rather than an established CSC-eradicating therapy, and its translational relevance requires validation in prospectively defined CSC models with pharmacologically justified delivery and exposure conditions.