Prevalence and Prognostic Significance of Positron Emission Tomography–Computed Tomography–Defined Low Skeletal Muscle Mass (Radiological Sarcopenia) in Metastatic Breast Cancer

Objective: Computed tomography–defined low skeletal muscle mass, often termed radiological sarcopenia in oncology, has been associated with adverse outcomes in several cancers, but its prognostic role in metastatic breast cancer (MBC) remains uncertain. The authors evaluated its prevalence and associations with clinicopathological features and survival in MBC. Methods: The authors retrospectively analyzed 61 women with MBC diagnosed during 2018-2023 who underwent positron emission tomography–computed tomography (PET-CT) at or near metastatic diagnosis. Low skeletal muscle index (SMI) was defined as <41 cm2/m2 and used as an imaging-based operational definition of sarcopenia; muscle strength and physical performance were unavailable. Logistic regression and Cox models assessed associated factors, diagnosis-based overall survival (OS), and first-line progression-free survival (PFS) (median follow-up, 35.5 months). Results: Low SMI was present in 33 of 61 patients (54.1%; 95% CI: 41.7-66.0). Higher body mass index was independently associated with lower odds of low SMI (odds ratio [OR]: 0.63; 95% CI: 0.47-0.84; P = .001). Low SMI was associated with worse diagnosis-based OS after adjustment (hazard ratio [HR]: 2.99; 95% CI: 1.08-8.28; P = .035), but not with first-line PFS (HR: 1.67; 95% CI: 0.87-3.19; P = .124). The analysis anchored to the PET-CT date did not confirm the OS association (adjusted HR: 2.15; 95% CI: 0.83-5.55; P = .115). Visceral metastasis was associated with shorter OS and PFS. Conclusion: Computed tomography-defined low skeletal muscle mass was common and associated with worse diagnosis-based OS, but the estimate was imprecise and was not confirmed in the date-anchored sensitivity analysis. These findings require confirmation in larger prospective cohorts using standardized muscle and functional assessments. Cite this article as: Güçlü Kantar T, Taş S, Doğan T, et al Prevalence and prognostic significance of positron emission tomography–computed tomography–defined low skeletal muscle mass (radiological sarcopenia) in metastatic breast cancer. Cerrahpaşa Med J 2026, 50, 0112, doi:10.5152/cjm.2026.26112.