Exploring the feasibility of exercise training during (neo)adjuvant chemotherapy in women with early- stage breast cancer: a pilot study examining immune and metabolic outcomes

Background: Immune function critically influences chemotherapy efficacy. Preclinical evidence is that exercise mobilizes NK and CD8 + T cells, enhances immunosurveillance, and improves treatment response. However, its immunological effects during chemotherapy for breast cancer remain poorly defined. Methods: This non-randomized pilot study examined a 12-week supervised combined aerobic and resistance exercise program during (neo)adjuvant treatment in women with early-stage breast cancer. Sessions were performed 2–3 times per week at moderate-to-vigorous intensity. Eleven patients (49.1 ± 14.4 years) completed the intervention and six (57.5 ± 5.4 years) served as a convenience control group for blood biomarkers. Outcomes included feasibility, immune cells, cytokines, metabolic biomarkers, body composition, quality of life, and fatigue. Results: Retention was 11/13 participants (84.6%), while attendance and adherence were 84 ± 23% and 78 ± 25%, respectively. Significant differences in immune cell subsets were observed, particularly within the CD8 + T-cell compartment. Compared with controls, exercisers showed a greater increase in CD8 + EMRA cells (p = 0.019) and a reduction in CD8+ naïve T cells (p = 0.029). Exercise prevented the insulin rise observed in controls (p = 0.034). Body weight and fat mass were maintained, with a signal toward increased lean mass (0.8 kg, p = 0.093). Exercise improved global quality of life (p = 0.031) and showed a signal toward reduced fatigue (p = 0.063). Conclusions: Supervised exercise during chemotherapy was feasible. Exploratory analyses suggest exercise may promote cytotoxic immune cell differentiation and mitigate metabolic dysregulation while improving quality of life. Larger trials are needed to confirm these findings.