Day-to-day cause-effect relations between cellular immune activity, fatigue and mood in a patient with prior breast cancer and current cancer-related fatigue and depression

This study of a breast cancer patient with cancer-related fatigue (CaRF) and depression investigated the bidirectional cause-effect relations between cellular immune activity, fatigue and mood during 'life as it is lived'. The 49-year-old patient (breast cancer diagnosis 5 years earlier, severe CaRF and increase in depressiveness since then) collected her entire urine for 28 days in 12-h intervals (from 8 p.m. to 8 a.m. and from 8 a.m. to 8 p.m.; total: 55 measurements) for the determination of urinary neopterin (immune activation marker) and creatinine levels using HPLC. Furthermore, she completed questionnaires twice each day (at approx. 8 a.m. and 8 p.m.), which yielded information on mood (3-Skalen-Eigenschaftswörterliste [EWL]) and fatigue levels (visual analog scale [VAS]). Cross-correlational analyses showed complex connections between urinary neopterin concentrations and mood and fatigue in terms of direction of effect, temporal delay and response pattern. Increases in urinary neopterin levels significantly preceded increases in fatigue intensity with a temporal delay of 60-72 h (lag 5: r = 0.298; p = 0.027), whereas increases in positive mood co-occurred with neopterin level increases (lag 0: r = +0.302; p = 0.025) and preceded decreases in neopterin concentrations with a temporal delay of 132-144 h (lag 11: r = -0.323; p = 0.017). These results confirm and extend our previous findings and show that in order to obtain an adequate understanding of the dynamic relations among cancer-related variables, the characteristics of everyday-life conditions need to be considered.