Purpose

Understanding the etiology of cancer-related fatigue (CRF) is critical to identify targets to develop therapies to reduce CRF burden. The goal of this systematic review was to expand on the initial work by the National Cancer Institute CRF Working Group to understand the state of the science related to the biology of CRF and, specifically, to evaluate studies that examined the relationships between biomarkers and CRF and to develop an etiologic model of CRF to guide researchers on pathways to explore or therapeutic targets to investigate.

Methods

This review was completed by the Multinational Association of Supportive Care in Cancer Fatigue Study Group-Biomarker Working Group. The initial search used three terms (biomarkers, fatigue, cancer), which yielded 11,129 articles. After removing duplicates, 9145 articles remained. Titles were assessed for the keywords "cancer" and "fatigue" resulting in 3811 articles. Articles published before 2010 and those with samples <50 were excluded, leaving 75 articles for full-text review. Of the 75 articles, 28 were further excluded for not investigating the associations of biomarkers and CRF.

Results

Of the 47 articles reviewed, 25 were cross-sectional and 22 were longitudinal studies. More than half (about 70 %) were published recently (2010-2013). Almost half (45 %) enrolled breast cancer participants. The majority of studies assessed fatigue using self-report questionnaires, and only two studies used clinical parameters to measure fatigue.

Conclusions

The findings from this review suggest that CRF is linked to immune/inflammatory, metabolic, neuroendocrine, and genetic biomarkers. We also identified gaps in knowledge and made recommendations for future research.

Cancer-related fatigue is defined as a distressing, persistent, subjective sense of physical, emotional, and/or cognitive tiredness or exhaustion related to cancer or cancer treatment that is not proportional to recent activity and interferes with usual functioning. It is one of the most common side effects in patients with cancer. Fatigue has been shown to be a consequence of active treatment, but it may also persist into posttreatment periods. Furthermore, difficulties in end-of-life care can be compounded by fatigue. The NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines) for Cancer-Related Fatigue provide guidance on screening for fatigue and recommendations for interventions based on the stage of treatment. Interventions may include education and counseling, general strategies for the management of fatigue, and specific nonpharmacologic and pharmacologic interventions. Fatigue is a frequently underreported complication in patients with cancer and, when reported, is responsible for reduced quality of life. Therefore, routine screening to identify fatigue is an important component in improving the quality of life for patients living with cancer.