Association of phase angle with muscle function and prognosis in patients with head and neck cancer undergoing chemoradiotherapy

•Phase angle was correlated with muscle mass/strength/quality and physical function indices.•Low phase angle was associated with severe anemia, aspiration, and treatment interruption.•Low phase angle was associated with poor 3-y survival. The aims of this study were to investigate the correlation of phase angle (PhA) with other parameters (e.g., muscle mass/quality/strength and physical function), assess the prognostic relevance of prechemoradiotherapy (CRT) PhA, and suggest a reference value of PhA in Asian patients with head and neck cancer (HNC). Ninety-six patients with HNC who underwent CRT were divided into two groups— maintained-PhA group and low-PhA group—according to the PhA 25th percentile values by sex. Pretreatment PhA was measured using direct segmental multifrequency bioelectrical impedance analysis, and muscle quality was assessed using echo intensity in ultrasound images. Correlation of PhA with other parameters was investigated, and between-group differences with respect to adverse events, treatment interruption, and 3-y survival were assessed. PhA showed a positive correlation with isometric knee extension force (R = 0.710), handgrip strength (R = 0.649), skeletal muscle mass index (R = 0.620), and maximum gait speed (R = 0.543; P < 0.001). PhA showed a negative correlation with echo intensity (R = −0.439) and five times sit-to-stand test (R = −0.505; P < 0.01). The low-PhA group had a higher incidence of severe anemia (52% in low-PhA versus 17% in maintained-PhA), aspiration (17 versus 1%), radiotherapy interruption (17 versus 3%), and poor 3-y survival (47 versus 81%) than the maintained-PhA group (P < 0.05). PhA was correlated with muscle mass/quality/strength, and physical function. Low PhA was associated with severe adverse events, treatment interruption, and shorter survival. These findings suggested that 4.6° for men and 4° for women may be useful as prognostic reference values in Asian patients with HNC.