Cancer-related fatigue (CRF) is more pervasive, debilitating, and longer lasting than normal fatigue and is not relieved by adequate sleep or rest. It is related to cancer or cancer treatment and may be a distressing, subjective sense of physical, emotional and/or cognitive tiredness or exhaustion not proportional to recent activity.r
The mechanisms responsible for cancer-related fatigue are poorly understood. Major obstacles to defining the relevant pathophysiology include the inherent subjectivity of fatigue, the difficulty in establishing objective behavioural correlates, and the wide variety of phenomena (including conditions that are unrelated to cancer or its treatment) that contribute to fatigue.r
Fatigue is a common side effect of cancer and cancer therapy.
Fatigue associated with cancer treatment can occur at any time during the treatment course and generally peaks 3 to 4 days following the nadir. It usually improves after treatment is completed, however it may persist for months or years.
In contrast, the intensity of CRF in patients undergoing radiotherapy (RT) typically peaks toward the end of therapy, gradually decreasing thereafter.r However, studies demonstrate that although CRF is most prevalent during active cancer therapy, a sense of fatigue may persist in survivors for months or even years after cessation of treatment.r
CRF is commonly cyclic and worst when blood counts are at their nadir (usually 10 to 14 days following treatment initiation). Haemoglobin levels below 90 g/L are often accompanied by fatigue.
Fatigue is more likely to occur in the presence of:
- cancer therapy, including:
- cytotoxic chemotherapy
- targeted therapies (small molecule tyrosine kinase inhibitors and monoclonal antibodies)
- radiotherapy (TBI)
- haemopoietic progenitor cell transplant (BMT)
- metastatic disease
- emotional distress, including depression and anxiety
- sleep disturbance
- nutritional deficiency, and/or fluid electrolyte imbalance
- nausea and vomiting
- medications, including: opioids, anti-histamines, anti-depressants and beta-blockers
- co-morbidities, including: hypothyroidism*, hypogonadism, uncontrolled diabetes, rheumatoid arthritis, adrenal insufficiency, cardiomyopathy, pulmonary dysfunction.
*Anticancer agents such as sunitinib or sorafenib can cause hypothyroidism.