Cancer-related fatigue and its impact on functioning.

This article presents the contrasting European and American perspectives on cancer-related fatigue (CRF) and its impact on functioning in cancer survivors. The content is presented in 3 sections: state of the art, intervention studies, and future areas of research, followed by a discussion. Gaps identified include a lack of understanding of the etiology, definition, and measurement of CRF. Models to guide the study of CRF, selection of biomarkers, and design of interventions are needed. There is overlap between Europe and the United States concerning the future directions for research and collaboration related to CRF. The authors suggest the need for international consensus regarding the defining features of CRF in cancer survivors to identify phenotypes, a harmonized measurement of CRF outcomes using instruments that have demonstrated measurement equivalence across languages and cultures, and interventions (including exercise, rehabilitation, and psychoeducational) that have been manualized to permit intervention fidelity across diverse contexts. Coordinated intercontinental efforts would increase understanding of the biological, psychological, and social mechanisms underlying CRF and assist in the design of future intervention studies as well as revisions to clinical guidelines.