Abstract Introduction: Adjuvant chemotherapy (AdjCTx) in breast cancer patients is associated with muscle weakness, fatigue, and functional decline that may persist into survivorship. While exercise is recognized as a supportive intervention, the role of circuit-based exercise (CBE) during active chemotherapy remains underexplored. This study investigated the feasibility and functional outcomes of a supervised CBE program in breast cancer patients with or without concurrent AdjCTx. Methods: This study included 40 postoperative breast cancer patients who completed a CBE program for at least two months between June 2020 and April 2023. Patients were stratified into AdjCTx (+) (n = 20) and AdjCTx (-) (n = 20) groups. The CBE protocol, delivered via the Milon® system, integrated aerobic and eccentric resistance training at 60% of one-repetition maximum. Functional outcomes included isokinetic knee extensor strength (peak torque), gait speed (10-meter walk test), balance (Berg Balance Scale), and mobility (Timed Up and Go). Body composition was assessed using bioelectrical impedance analysis. Within-and between-group changes were analyzed using repeated measures ANOVA and paired t-tests. Results: Both groups demonstrated significant improvements in knee extensor strength over time (P 0.05), with significant time effects (F = 10.75-12.34, P 0.001). The AdjCTx (-) group demonstrated greater absolute gains, while the AdjCTx (+) group showed steady, progressive improvements without regression. BMI significantly decreased in both groups (P0.001); changes in body fat percentage and ALMI were not statistically significant. Functional improvements in TUG and BBS were observed only in the AdjCTx (-) group (P0.05), whereas the AdjCTx (+) group maintained baseline function. Gait speed improved significantly in both groups, with a greater increase in the AdjCTx (+) group (P=0.022), despite persistent strength deficits. Conclusions: CBE incorporating eccentric resistance is a feasible and well-tolerated during AdjCTx. It preserves lower-limb strength and functional capacity, highlighting its potential as an early, structured rehabilitation strategy to counteract treatment-related decline and support long-term survivorship in breast cancer patients. Citation Format: K. Cho, E. Han, S. IM. Impact of circuit based exercise in breast cancer survivorship abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS1-05-17.
Cho et al. (Tue,) studied this question.