Abstract / Summary
Abstract Purpose To characterise treatment burden regarding adverse events, relative dose intensity and treatment modifications and their associations with body composition, physical activity, and paclitaxel exposure in breast cancer patients. Methods This prospective cohort included 20 women with breast cancer receiving 12 cycles of weekly paclitaxel. Body composition was assessed by computed tomography, dual-energy X-ray absorptiometry, and bioelectrical impedance; physical activity by accelerometry. Patient-reported outcomes, medical-record adverse events, relative dose intensity, treatment modifications and paclitaxel concentrations were documented. Baseline-adjusted mixed-effects models examined body composition and physical activity markers. Results From baseline to final follow-up, sensory neuropathy and fatigue increased by 10.0, 95% CI [4.8, 15.1] and 19.4 points, 95% CI [9.5, 29.3], while physical functioning and global health declined by 10.4, 95% CI [2.8, 18.0] and 10.7 points, 95% CI [1.5–19.8]. No adverse event reached Common Terminology Criteria for Adverse Events grade ≥ 3; yet 65% of participants had a toxicity-attributed treatment modification. Higher adiposity markers across imaging modalities and body mass index were associated with worse sensory neuropathy. Per 1,000 additional steps/day, fatigue was 4.54 points lower, 95% CI [− 8.42, − 0.66], physical functioning 1.92 higher, 95% CI [0.23, 3.61], and global health 2.48 higher, 95% CI [0.33, 4.63]. No consistent associations were observed with relative dose intensity, modification count, or adverse-event burden. Conclusion Weekly paclitaxel was accompanied by clinically important patient-reported deterioration and frequent treatment modifications despite no CTCAE grade ≥ 3 events. Greater adiposity and lower physical activity were associated with higher patient-reported burden; the design does not support causal or clinical inference. Trial registration ClinicalTrials.gov NCT06387901, registered 29 April 2024.