Longitudinal associations of bioelectrical phase angle and fatigue in breast cancer patients.

Cancer-related fatigue is commonly treated in an undifferentiated manner, because its pathophysiology is still not well understood. Therefore, we investigated if bioelectrical phase angle (PhA), a non-invasive marker of cell integrity, could help to single out specific fatigue subtypes. In a randomized controlled strength training intervention trial, PhA was measured by bioelectrical impedance analysis in 158 breast cancer patients. Fatigue was assessed with the multidimensional 20-item Fatigue Assessment Questionnaire. Multiple regression analyses considering changes in PhA and fatigue from baseline to post-intervention and ANCOVA models investigating the strength training effect on PhA were conducted. Further, explorative mediation and moderation analyses were performed. Decrease (=worsening) in PhA was significantly associated with increase in physical (P = .010) and emotional (P = .019) fatigue. These associations were markedly stronger in patients with normal BMI (interaction P = .059 and .097) and with low pre-diagnosis exercise level (interaction P = .058 and .19). Among patients with normal BMI strength training was associated with an increase in PhA (ANCOVA P = .059), but not among overweight/obese patients (interaction P = .035). Chemotherapy was a major determinant for low PhA, but PhA did not mediate the effect of chemotherapy on fatigue. In conclusion, PhA has a significant inverse association with physical and emotional fatigue. This association is moderated by BMI and previous exercise. Significant relationships of PhA were also observed with chemotherapy and strength training. Thus, PhA might be a marker that could help in the classification of subtypes of fatigue with different pathophysiology, which may require specifically tailored treatment. Further research on this is warranted.