Fatigue is one of the most common symptoms for patients with cancer, reported in up to 90% of patients undergoing chemotherapy or radiation therapy. Patients who are cancer survivors can still be affected by fatigue months to even years out from their last treatment. Cancer-related fatigue (CRF) specifically refers to the distressing tiredness or decreased energy out of proportion to activity associated with cancer or cancer therapy. It does not respond to rest. It can affect concentration, sleep patterns, and emotional coping, separate from depression. It is also a symptom that is easily overlooked, as it is often “expected” or assumed to occur alongside treatment, and patients with non-cancer diseases also experience fatigue.
In cancer, there can be many contributing factors to the fatigue that patients experience, and oftentimes, the fatigue is from multiple causes, both directly and indirectly related to the cancer. As many patients experience, the cancer itself can cause physiologic problems, such as anemia or electrolyte imbalances (think of sodium or calcium), or these chemical changes can occur from cancer treatments. For both chemotherapy and radiation therapy, fatigue is a known side effect; in chemotherapy, it tends to be more concurrent with treatment or immediately in the days afterwards between cycles; in radiation therapy, the fatigue tends to accumulate throughout the course of the radiation. Pain, if not controlled, can contribute to fatigue. It is also known that in advanced cancer, fatigue is caused by a metabolic syndrome of the cancer, similar to how loss of appetite and weight loss are also caused by this same metabolic syndrome. If patients are hospitalized due to complications like infections, this can cause both fatigue during the hospitalization as well as afterwards due to deconditioning (generalized weakness after a prolonged period of decreased mobility).
