Impact and Mechanisms of Cognitive Behavioural Therapy for Insomnia on Fatigue among Cancer Survivors: A Secondary Analysis of a Randomized Controlled Trial.

Study objectives: Cancer-related fatigue is one of the most common symptoms in cancer survivors. Cognitive behavioural therapy for insomnia (CBT-I) can improve fatigue, but mechanisms are unclear. This secondary analysis of a randomized controlled trial evaluated whether CBT-I led to a significant improvement in fatigue, accounting for change in comorbid symptoms of insomnia, perceived cognitive impairment (PCI), anxiety, and depression. The parent study evaluated the impacts of CBT-I on PCI and insomnia.

Methods: Cancer survivors with insomnia and PCI were randomized to CBT-I or a sleep-self monitoring waitlist control. Fatigue was measured using the Multidimensional Fatigue Symptom Inventory - Short Form at pre-, mid-, and post-treatment. Significant improvement in fatigue was defined as a reduction >10.79 points. Insomnia, PCI, anxiety and depression symptoms were assessed. A linear mixed model evaluated whether CBT-I improved fatigue after adjusting for comorbidities. Mediation analyses examined whether change in comorbidities accounted for the effect of CBT-I on fatigue.

Results: The sample consisted of 132 cancer survivors (77% female, Mage=60.12 years, 41% breast cancer). There was a significant group-by-time interaction on fatigue, p<.001, with the CBT-I group experiencing a 20.6-point reduction in fatigue compared to 3.7-points in the control. Improvements in fatigue were fully accounted for by improvements in the comorbidities with change in insomnia accounting for 45.3% of the effect observed in fatigue.

Conclusions: CBT-I resulted in significant improvement in fatigue, and these effects were largely accounted for by change in insomnia. CBT-I is a robust intervention with efficacy for improving fatigue among cancer survivors.