This review compares the efficacy and adverse effects of specific erythropoietic stimulants (i.e., epoetin alfa or beta], darbepoetin alfa) when used to manage anemia in patients undergoing cancer therapy (i.e., chemotherapy and/or radiation). This review also addresses questions relevant to optimizing the use of erythropoietic stimulants as a general class: the outcomes of using alternative thresholds to initiate or discontinue treatment and whether there are early predictors of response to treatment. Erythropoietin is an endogenous hormone, produced primarily in the kidney, which participates in regulating red blood cell production (erythropoiesis). Two forms of recombinant human erythropoietin-epoetin alfa and epoetin beta (the latter not commercially available in the United States)-have been extensively studied and used clinically for more than a decade to treat various anemias; they have similar clinical efficacy. In a recent review of safety concerns associated with recombinant human erythropoietins, a U.S. Food and Drug Administration (FDA) briefing document noted that ..".the biochemical differences between various erythropoietin products are not associated with marked differences in the pharmacodynamic properties of the different products when used at recommended doses, thus effects observed with these non-US-licensed products may also be associated with the U.S. licensed product." Anemia (deficiency of red blood cells) occurs in 13-78 percent of patients undergoing treatment for solid tumors and 30-40 percent of patients treated for lymphoma. Tumor type, treatment regimen, and history of prior cancer therapy influence the risk and severity of anemia. This report focuses on use of epoetin or darbepoetin to manage anemia in patients undergoing cancer treatment with chemotherapy and/or radiation. Anemia severity is defined by hemoglobin (Hb) concentration. Erythropoietin, a hormone produced primarily in the kidney, participates in regulating red blood cell production (erythropoiesis) and thus Hb concentration. Two erythropoietic stimulants are available commercially in the United States, epoetin alfa (Epogen(r), Procrit(r)) and darbepoetin alfa (Aranesp(r)), which is a newer and longer acting drug. Epoetin beta, which is pharmacologically and clinically similar to epoetin alfa, is commercially available in Europe and elsewhere. Erythropoietic stimulants are widely used in clinical practice to manage anemia of patients undergoing cancer treatment and to reduce the need for transfusion. Although it is well established that erythropoietic stimulants improve anemia in patients undergoing cancer treatment, the comparative effectiveness of epoetin and darbepoetin has not been evaluated in a systematic review. Moreover, trials varied substantially in how erythropoietic stimulants have been used, including Hb concentration at start of treatment, doses given, treatment duration, and target Hb concentrations they sought to maintain. A review of these various trials may help maximize benefit, optimize drug usage, and minimize adverse effects from using erythropoietic stimulants to manage anemia in patients undergoing cancer treatment. The report addresses the following questions: 1. What are the comparative efficacy and safety of epoetin (alfa or beta) and darbepoetin? 2. How do alternative dosing strategies affect the comparative efficacy and safety of epoetin and darbepoetin? 3. How do alternative thresholds for initiating treatment or alternative criteria for discontinuing therapy or duration of therapy affect the efficacy and safety of erythropoietic stimulants? 4. Are any patient characteristics at baseline or early hematologic changes useful to select patients or predict responses to treatment with erythropoietic stimu