Prediction of response to optimize outcome of treatment with erythropoietin.

Recombinant human erythropoietin (EPO; epoetin) has been shown to be effective in improving anemia in a proportion of cancer patients. The response rate is approximately 60%, but varies considerably according to baseline hematocrit and transfusion needs, as well as the response criteria used. Response is not greatly influenced by the type of tumor, except in situations of major marrow involvement and limited residual hematopoiesis, or in the presence of specific mechanisms of anemia, such as hemolysis, splenomegaly, bleeding, hemodilution, or ineffective erythropoiesis. Stem cell damage by previous therapy as well as marrow suppression by current intensive chemotherapy can impair response. Besides its intensity, the type of chemotherapy may not be critical, although patients undergoing platinum-based chemotherapy may respond faster than those receiving non-platinum regimens. Complications, such as infections, bleeding, or nutritional deficiencies, may have a major negative impact on outcome. An important response-limiting factor is functional iron deficiency (ie, an imbalance between iron needs in the erythropoietic marrow and iron supply), which depends on the level of iron stores and its rate of mobilization. Functional iron deficiency is best monitored by the percentage of hypochromic red blood cells, and oral or intravenous iron supplements should be given when this percentage increases above 10%. All these factors explain why the response rate to epoetin is only approximately 60%. Therefore, it would be interesting to develop models that could help predict response to epoetin to help select the most appropriate cancer patients for this therapy. Few baseline parameters have been shown to be highly predictive of response in patients with solid tumors, although most studies in patients with myeloma or lymphoma have indicated that patients with a low baseline serum EPO level will respond better. Early changes after 2 to 4 weeks of treatment are also of great interest. Among these early changes, increments of soluble transferrin receptor, reticulocytes, and hemoglobin, as well as the persistence of elevated ferritin or EPO levels, have all shown some predictive value. Combination of baseline serum EPO and the 2-week increment of soluble transferrin receptor or hemoglobin may provide the best prediction of response.