Cognitive and mood disturbance as causes and symptoms of fatigue in cancer patients.

Fatigue, cognitive dysfunction, and depression are very common in cancer patients. A relationship among the three entities is recognized but poorly understood. Factors that contribute to this poor understanding are the subjective nature of the symptoms, multiple potential causes, and a lack of reliable assessment tools. An understanding of fatigue in cancer patients may benefit from studies of chronic fatigue syndrome (CFS) and other nonmalignant diseases indicating that cognitive impairment varies with physical and mental fatigue, and that symptoms of depression experienced by patients with physical illnesses and primary mood disorders are qualitatively different. The multidimensional nature of fatigue suggests that interventions should be patient-specific. They could be related to lifestyle or involve the use of specific behavioral or pharmacologic therapies. As is the case with depression and cognitive disorders, targeted interventions against cancer-related fatigue will benefit from a better understanding of its potential biologic causes. Consideration of cognitive dysfunction and depression complicates the understanding of cancer-related fatigue; however, it provides opportunities to assist patients who must deal with this serious problem.