The level of serum erythropoietin (sEPO) is a strong predictor of clinical response to ESAs; patients with lower-risk MDS with a sEPO level of <100 U/l have a response rate of >70%, whereas, for those patients with a sEPO level of >500 U/l, the response rate is <10% [45]. This evidence concerns the gene EPO and myelodysplastic syndrome.