Resistance Exercise Training Selectively Modulates Tumor Suppressor and Muscle-Regulatory MicroRNAs in Breast Cancer Survivors and Healthy Postmenopausal Women: An Exploratory Study

Progressive resistance exercise training (RET) enhances skeletal muscle mass in healthy postmenopausal women (HEAs) and breast cancer survivors (BCSs) undergoing endocrine therapy. MicroRNAs (miRNAs) are recognized as key epigenetic regulators of exercise-induced adaptations, functioning as tumor suppressors, oncomiRs, and modulators of skeletal muscle homeostasis. Nevertheless, the impact of RET on circulating miRNA profiles in this population remains largely unexplored. This study aimed to explore the effects of a 12-week progressive RET program on plasma miRNAs associated with tumor biology and skeletal muscle regulation in HEAs and BCSs. Five HEAs and five BCSs undergoing endocrine therapy completed a 12-week supervised progressive RET program (3 sessions/week, 60–80% 1RM). Plasma samples were collected before and after intervention, and candidate miRNA expression was quantified by qRT-PCR, normalized to hsa-miR-16-5p, and analyzed using the 2−ΔΔCt method. At baseline, no significant differences were observed between HEA and BCS in tumor suppressor miRNAs (miR-let-7f-5p, miR-125a-5p, miR-342-3p), oncomiRs (miR-21-5p, miR-155-5p, miR-221-3p), or skeletal muscle–related miRNAs (miR-206-3p, miR-486-5p) (p > 0.05). The only exception was miR-375-3p, which showed increased expression in HEA vs BCS (p = 0.037). After 12 weeks of RET, The BCS group showed increases in miR-125a-5p (p = 0.050) and miR-342-3p (p = 0.048) with significant group × time interactions that remained significant after Benjamini–Hochberg False Discovery Rate (BH-FDR) correction (FDR-adjusted p = 0.042 for both). Both groups displayed a nominal increase in miR-375-3p (p = 0.042), which did not remain significant after FDR correction. No significant changes were detected for miR-let-7f-5p or the analyzed oncomiRs in either group. Both miR-206-3p and miR-486-5p exhibited upward trends in the BCS group (p > 0.05). In this exploratory study, 12-week RET program was associated with selective changes in plasma miRNA expression in the HEA and BCS groups, suggesting that this training regimen may act as an epigenetic modulator of circulating miRNAs involved in tumor suppression and skeletal muscle homeostasis.