Changes in bioelectrical impedance during chemotherapy in women with early breast cancer

Introduction Body composition changes during chemotherapy for early breast cancer (EBC) affect treatment tolerance and outcomes. Bioelectrical Impedance Analysis (BIA) provides a rapid, non-invasive assessment of the physiological state, but its utility rests on assumptions that may be violated during active treatment. Methods In this prospective, single center observational pilot study, 32 women with EBC receiving four to six cycles of (neo)adjuvant FEC-T chemotherapy underwent serial BIA measurements (seca mBCA515) before each cycle and 3 weeks after completing chemotherapy. Impedance measures (resistance, reactance, Impedance Ratio, Phase Angle) were expressed as age- and sex-standardized SD Scores. Results Mean impedance values at baseline lay within the reference range (±2 SDS), although Phase Angle was already significantly below the reference mean before treatment. With successive chemotherapy cycles, Standardized Phase Angle declined significantly after the third cycle (mean decrease 1.41 SD, −10.3%; p < 0.001). Standardized Impedance Ratio rose progressively, while Resistance and Reactance fell. By cycle six, 13 women exceeded the upper reference limit for Impedance Ratio and 17 fell below the lower limit for Phase Angle. These changes indicate major fluid redistribution, which violates assumptions required for BIA-derived body composition estimation. Discussion It is feasible to integrate BIA measurement into routine chemotherapy care for EBC. The results reveal progressive, clinically meaningful changes in impedance with each treatment cycle. The assumptions underlying BIA-derived body composition estimates are upheld before treatment but not during chemotherapy. Phase Angle shows the greatest sensitivity to these changes and warrants prospective evaluation as a predictor of chemotherapy toxicity.