Fatigue and Circadian Activity Rhythms in Breast Cancer Patients Before and After Chemotherapy: A Controlled Study

BACKGROUND: Breast cancer (BC) patients often experience cancer-related fatigue (CRF) before, during, and after their chemotherapy. Circadian rhythms are 24-hour cycles of behavior and physiology that are generated by internal pacemakers and entrained by zeitgebers (e.g., light). A few studies have suggested a relationship between fatigue and circadian rhythms in some clinical populations. METHODS: One hundred and forty-eight women diagnosed with stage I-III breast cancer and scheduled to receive at least four cycles of adjuvant or neoadjuvant chemotherapy, and 61 controls (cancer-free healthy women) participated in this study. Data were collected before (Baseline) and after four cycles of chemotherapy (Cycle-4). Fatigue was assessed with the Short Form of Multidimensional Fatigue Symptom Inventory (MFSI-SF); circadian activity rhythm (CAR) was recorded with wrist actigraphy (six parameters included: amplitude, acrophase, mesor, up-mesor, down-mesor and F-statistic). A mixed model analysis was used to examine changes in fatigue and CAR parameters compared to controls, and to examine the longitudinal relationship between fatigue and CAR parameters in BC patients. RESULTS: More severe CRF (total and subscale scores) and disrupted CAR (amplitude, mesor and F-statistic) were observed in BC patients compared to controls at both Baseline and Cycle-4 (all p's<0.05); BC patients also experienced more fatigue and decreased amplitude and mesor, as well as delayed up-mesor time at Cycle-4 compared to Baseline (all p's<0.05). The increased total MFSI-SF scores were significantly associated with decreased amplitude, mesor and F-statistic (all p's<0.006). CONCLUSION: CRF exists and CAR is disrupted even before the start of chemotherapy. The significant relationship between CRF and CAR indicate possible underlying connections. Re-entraining the disturbed CAR using effective interventions such as bright light therapy might also improve CRF.