Cancer-related fatigue, depressive symptoms, and functional status: a mediation model

Patients with cancer grapple with a confusing array of disease- and treatment-related symptoms while trying to maintain functioning in usual roles and daily activities. Research is needed to sort out and identify symptom clusters as a basis for a rational approach to symptom management.

The aim of this study was to test, through secondary analysis, a mediation hypothesis about the direct and indirect relationships between fatigue and depressive symptoms through a pathway involving functional status.

Data from the experimental and control groups of a randomized clinical intervention trial for fatigue management, collected after the second chemotherapy treatment or during the last week of radiotherapy, were analyzed. The mediation pathway from fatigue to depressive symptoms through functional status was tested separately for groups receiving either an energy conservation intervention or a control intervention, equating for time and attention.

For the control group, the results indicate support for partial mediation. The previously significant relationship between fatigue and depressive symptoms was reduced after functional status was controlled, accounting for 43% of the total mediated effect. The mediation hypothesis was not supported in the energy conservation group, indicating that the intervention may have changed the role of functional status in mediating the effect of fatigue on depressive symptoms.

In the control group, when routine activities became more difficult because of fatigue, individuals had more depressive symptoms. The results suggest that functional status is an important factor to consider in symptom management for fatigue. An appropriate intervention for fatigue would have two targets: the fatigue and strategies to reduce the likelihood of impaired functioning that could result in elevated depressive symptoms.