Fatigue experienced as a side effect of cancer treatment is differentiated from fatigue experienced by healthy people in their daily lives. Healthy fatigue is frequently described as acute fatigue that is eventually relieved by sleep and rest; cancer treatment–related fatigue is categorized as chronic fatigue because it is present over a long period of time, interferes with functioning, and is not completely relieved by sleep and rest. Also, the level of CRF is often disproportionate to the level of activity or energy exerted. Although the label chronic fatigue is accurate, using this label does not mean that people with cancer who experience fatigue have chronic fatigue syndrome. Using the phrase chronic fatigue can be confusing to both patients and health professionals. Terms such as cancer fatigue, cancer-related fatigue, and cancer treatment–related fatigue have all been used in the clinical literature, research literature, and educational materials for patients and the public.
Fatigue has a negative impact on all areas of function, including mood, physical function, work performance, social interaction, family care, cognitive performance, school work, community activities, and sense of self.[15,16,17,18] The pattern of fatigue associated with cancer treatment varies according to type and schedule of treatment. For example, people treated with cyclic chemotherapy regimens generally exhibit peak fatigue in the days following treatment, then report lower levels of fatigue until the next treatment; however, those receiving external-beam radiation therapy report gradually increasing fatigue over the course of therapy of the largest treatment field. Few studies of people receiving cancer treatment have addressed the issue of fatigue as a result of the emotional distress associated with undergoing a diagnostic evaluation for cancer and the effects of medical and surgical procedures used for that evaluation and for initial treatment. Because most adults enter the cancer care system following at least one surgical procedure and because surgery and emotional distress are both associated with fatigue, it is likely that most people beginning nonsurgical treatment are experiencing fatigue at the beginning of treatment.[19,20]
Recommendations for fatigue management focus on identifying factors that may be contributing to fatigue. Because the only definitive causal mechanism demonstrated through research to date is chemotherapy-induced anemia, most clinical recommendations for managing fatigue caused by something other than chemotherapy-induced anemia rely on careful development of clinical hypotheses, as outlined in the National Comprehensive Cancer Network guidelines on fatigue. The only level 1 intervention for CRF at this time is exercise. (Refer to the Exercise section of this summary for more information.) Much more research is needed to better define fatigue and its trajectory, understand its physiology, and determine the best ways to prevent and treat it.