<qa>  What is a protein that stimulates platelet production?Platelets are cells that help make the blood clot. A decrease in platelets can cause bleeding, which may prevent or delay a patient from receiving chemotherapy. R-HyperCVAD rituximab, cyclophosphamide, vincristine, doxorubicin, and dexamethasone and R-Ara-CMTX rituximab, cytarabine, and methotrexate are two chemotherapy regimens that are known to increase the risk of lower platelet counts. Researchers want to find out if AMG 531 can lower the risk and severity of this side effect. AMG 531 is a protein that stimulates platelet production. 