Skeletal Muscle Loss During Neoadjuvant Chemotherapy for Breast Cancer: Diabetes as an Independent Predictor

This study examined body composition changes during neoadjuvant chemotherapy (NACT) for breast cancer and aimed to identify clinical parameters associated with skeletal muscle loss.

We retrospectively analyzed women with stage I-III breast cancer who received NACT. Skeletal muscle and subcutaneous fat areas at the third lumbar vertebra were quantified on computed tomography and normalized for height to calculate the skeletal muscle index (SMI, cm²/m²) and subcutaneous fat index (SFI, cm²/m²). Pre- and post-NACT values were compared, and the prevalence of low skeletal muscle mass (LSMM, SMI <38.5 cm²/m²) and sarcopenic obesity (body mass index ≥30 kg/m² with LSMM) was determined. Multivariable linear regression assessed independent predictors of post-NACT SMI.

A total of 177 patients (mean age 51.0±10.7 years; 24% with diabetes) were included. Mean SMI declined significantly after NACT (43.1±7.4 to 41.4±7.1 cm²/m²; mean change -1.7±3.1, p<0.001). SFI also decreased (132.9±59.2 to 123.5±55.1 cm²/m²; mean change -9.5±27.0, p<0.001). The prevalence of LSMM increased from 27.7% to 37.3% (p = 0.003), and sarcopenic obesity from 8.5% to 12.4%. Patients with diabetes experienced greater muscle loss than those without diabetes (-2.7 vs. -1.4 cm²/m²). Diabetes mellitus was the only independent predictor of post-NACT SMI decline (β = -1.42, p = 0.013), while age and chemotherapy regimen were not significant.

NACT is associated with significant reductions in skeletal muscle and subcutaneous fat, together with increased rates of LSMM. Diabetes mellitus independently predicted lower post-treatment SMI.