Phase Angle as an Early Functional Biomarker of Cancer‐Related Fatigue in Pediatric Oncology: A Prospective Longitudinal Study

BACKGROUND: Pediatric cancer remains a leading cause of morbidity and mortality worldwide, particularly in low-and middle-income countries. Cancer treatment may impair nutritional status, alter body composition, and exacerbate cancer-related fatigue (CRF). Phase angle (PhA), a bioelectrical impedance-derived marker of cellular integrity, has emerged as a potential noninvasive indicator associated with functional status, yet its role in pediatric oncology remains underexplored. OBJECTIVE: To investigate longitudinal changes in nutritional status and CRF and to examine the association between PhA and CRF in children/adolescents with cancer during the first 3 months of treatment. METHODS: Prospective longitudinal study included children/adolescents (0-18 years) newly diagnosed with cancer or central nervous system (CNS) tumors. Participants were assessed at diagnosis-[T0], 1 month-[T1], and 3 months-[T2] after treatment initiation. Data collected included clinical/sociodemographic characteristics, nutritional status (anthropometry/STRONGkids), body composition, and CRF (PedsQLMFS). Repeated measures analyses and linear mixed models were performed, with α = 5%. RESULTS: A total of 23 patients (mean age 5.7 years old; 65.2% female) were included. Over time, significant reductions were observed in body mass index (p = 0.044), PhA (p = 0.013), and lean mass (p = 0.037). Self-reported fatigue worsened, particularly in the general fatigue domain (p = 0.043). Correlation analyses demonstrated significant associations between fatigue and body composition indicators, particularly calf circumference (r = 0.809-0.861), body fat mass (r = 0.756-0.844), and PhA (r = 0.521-0.752) in self-reports. In linear mixed-effects models, PhA was independently associated with total fatigue over time (β = 19.97; p = 0.011). CONCLUSIONS: Children and adolescents undergoing cancer treatment experience early deterioration in nutritional status and body composition, accompanied by worsening CRF. Fatigue was consistently associated with PhA and lean mass-related indicators, suggesting that body composition and cellular integrity may be associated with fatigue severity during treatment. PhA emerged as a particularly promising noninvasive marker, independently associated with fatigue over time. These findings support the incorporation of PhA and comprehensive nutritional assessment beyond conventional weight- and height-based measures to improve the early identification of patients at risk.