Erythropoietin receptors on tumor cells: what do they mean?

Given the apparent presence of erythropoietin receptors (EPORs) in cancer tissues, questions have been raised about the possible influence of erythropoiesis-stimulating agents (ESAs) on tumor growth and proliferation. Preclinical studies of ESAs have shown no greater tumor proliferation in cell lines and no adverse effect on treatment outcomes in animal models. Furthermore, it appears that the commercially available antibodies that have been used in clinical studies are not specific to EPORs. In particular, they detect isoforms of heat shock protein 70, which is found in tumor cells and is associated with poor prognosis. For this reason, results from clinical studies purporting to relate the administration of ESAs to shorter survival must be considered inconclusive and complicated by methodological and sampling issues. Ongoing studies will help clarify whether the existence of the EPOR has any relevance at all in the cancer setting.