Fatigue is often overlooked in the assessment although it is one of the most common complaints of the patients with cancer. It is a subjective and nonspecific complaint, which negatively affects the life of the patient. Mechanisms of fatigue are multifactorial. Chronic illnesses, treatment modalities, complications (anemia, metabolic abnormalities, …) or psychological stress may cause fatigue. Fatigue developing during chemotherapy or radiotherapy may depend on the treatment modalities administered, however, it is not easy to explain the etiology of fatigue persisting after the end of treatment. Fatigue has been found to be as a factor affecting survival negatively in studies where predicted survival is 100 days. However, most of the studies performed on patients with a predicted survival of 30 days failed to find fatigue as a major predictor of survival. Fatigue loses its prognostic significance since almost all patients with short-term survival have fatigue. Currently there are many questions remained unanswered about the pathophysiology and treatment of the fatigue in cancer patients. Why do patients continue to experience fatigue months or even years following the diagnosis and treatment of cancer? Which treatment modalities are effective in preventing or reducing fatigue? Will the treatment of fatigue be able to improve survival in patients with cancer?

Keywords: Supportive care, fatigue, cancer, weakness