Novel insights into phase angle in breast cancer - stage-specific associations between body composition and metabolic age.

Background: Body composition parameters are critical in determining overall health in breast cancer (BC) patients. Phase angle (PhA), measured via non-invasive Bioelectrical Impedance Analysis (BIA), is emerging as a superior biomarker compared to body mass index (BMI). This study examined the relationship between PhA and body composition across different BC stages. Materials and methods: Bioelectrical impedance analysis was performed in 833 BC patients who were stratified into early-, intermediate-, and advanced-stage groups based on TNM (tumour, node, metastasis) classification and treatment approach. Body composition parameters, including water compartments, muscle mass, and metabolic age, were analysed and compared between groups. Results: Phase angle differed significantly across cancer stages (p = 0.0065) and was correlated with age independently of stage (p = 0.0033). Differences in extracellular water (ECW; p = 0.0392), intracellular water (ICW; p = 0.0014), total body water (TBW; p = 0.0069), and muscle mass (p = 0.0085) were observed between stages. Phase angle was significantly associated with ICW across all stages, with additional correlations found between PhA and predicted muscle mass (PMM), as well as TBW, in early- and intermediate-stage patients. Metabolic age varied by cancer stage (p = 0.0052) and influenced PhA independently of stage (p = 0.1906), with higher PhA observed in patients metabolically older than their chronological age. Conclusions: Phase angle is closely linked to key body composition parameters, particularly water and muscle content, with some associations varying by cancer stage. This is the first study to report a stage-independent relationship between PhA and metabolic age in BC patients, warranting further investigation into its clinical relevance.