EPO's alter ego: erythropoietin has multiple actions.

Many cancer patients suffer from anemia, which has a major detrimental effect on their quality of life. Recombinant human erythropoietin (rHuEPO) is now widely used in cancer patients, as it improves hematocrit, lowers blood transfusion requirements, and improves quality of life. Recent research indicates that EPO has pleiotropic effects on the body well beyond the maintenance of red cell mass, but the mechanisms involved in relieving fatigue and improving quality of life in cancer patients are poorly understood. EPO receptors (EPO-Rs) have been detected in many different cells and tissues, providing evidence for autocrine, paracrine, and endocrine functions of EPO. Apart from its endocrine function, EPO may have a generalized role as an antiapoptotic agent that is associated with enhancement of muscle tone, mucosal status, and gonadal and cognitive function. The recent discovery of EPO-Rs in breast tumor vasculature, while raising important questions about the possible effects of pharmacological doses of rHuEPO on tumor cells, also suggests that the receptors could provide a useful target for drugs attached to EPO.