Fatigue: a main component of anemia symptomatology.

Fatigue is a common complaint of patients with cancer or other physical or mental disorders. In cancer patients, the estimated prevalence of fatigue is high (about 70% to 90% in different surveys). However, despite the high prevalence and widely recognized clinical relevance of fatigue, few studies have been performed to evaluate the putative causal factors and therapeutic approaches for this condition. The paucity of studies has been mainly because of the lack of proper instruments to quantify this clinical problem. Moreover, fatigue is multifactorial, which makes evaluation of precise relationships with other medical conditions difficult. In particular, fatigue is considered the cardinal symptom of anemia. The pathogenesis of anemia-related fatigue remains unclear, but some suggest that abnormalities in energy metabolism play a role in inducing fatigue. In cancer patients, this effect may be exacerbated by the increased metabolic needs associated with tumor growth. At the clinical level, the relationship between anemia and fatigue is universally accepted. However, early studies were unable to show a clear association between fatigue and hemoglobin levels. Recently, new insights were afforded by the implementation of innovative survey instruments that assess the effects of fatigue and other (nonfatigue) symptoms of anemia on the patient's well-being and quality of life. The use of these validated instruments has shown a direct effect of hemoglobin levels on fatigue and other quality of life parameters. Thus, amelioration of anemia and fatigue should be considered a primary endpoint of antineoplastic and supportive-care treatment of cancer patients. Accordingly, the search for new simplified methods of assessment of fatigue and other anemia-related symptoms and their treatment outcomes should be strongly encouraged.