Background/Objectives: Sarcopenia, defined by reduced skeletal muscle mass, may have prognostic relevance in metastatic breast cancer. Muscle quality, reflected by adipose tissue indices, could also influence outcomes, but evidence in CDK4/6 (cyclin-dependent kinase)-inhibitor-treated patients is limited. We therefore evaluated the prognostic impact of baseline sarcopenia and adipose tissue distribution indices in this population. Methods: We retrospectively analyzed 156 women with HR+/HER2− MBC (hormone-receptor-positive, Her2-negative metastatic breast cancer) who initiated ribociclib or palbociclib plus endocrine therapy between May 2020 and January 2024. Association between L3 computed tomography (CT)-derived skeletal muscle index (SMI) and adipose tissue indices was evaluated with univariable and multivariable analyses. Sarcopenia was defined as SMI < 41 cm2/m2. Results: Median age was 57.6 years; 75% of patients were postmenopausal, and 48% of the cohort were sarcopenic. Median progression-free survival (PFS) for the entire cohort was 24.7 months (95% CI: 20.3–29.2). Patients with baseline sarcopenia had substantially shorter PFS compared to those without sarcopenia (21.5 months (95% CI: 10.9–32.1), versus 27.1 months (95% CI: 15.2–39; p = 0.016). Multivariable Cox regression analyses identified two independent predictors of prolonged PFS: non-sarcopenia (SMI ≥ 41 cm2/m2) and de novo metastatic disease. BMI (body mass index) and all adipose indices were not associated with PFS. Conclusions: Baseline non-sarcopenia and de novo metastatic disease independently predict longer PFS on CDK4/6 inhibitors, whereas adiposity measures and BMI are not prognostic. Routine body composition assessment may refine risk stratification and identify candidates for supportive interventions. Prospective studies are needed to validate these findings.
Karahan et al. (Fri,) studied this question.