Platelets are tiny cells produced in the bone marrow and released into the bloodstream, where they help the blood to clot. The risk for bleeding is therefore increased in patients with low platelet counts. Many cancer chemotherapies interfere with platelet production; a low platelet count (thrombocytopenia) is therefore a common side effect of chemotherapy. Platelet transfusions are used to treat dangerously low platelet counts. Unfortunately, such transfusions can result in transfusion reactions or infection; they are also quite expensive. Moreover, some patients stop responding to platelet transfusions after a while. Carboplatin is a drug that can be effective as chemotherapy for cancers of the ovaries and uterus. However, low platelet counts often complicate treatment with carboplatin. Thrombopoietin is a naturally occurring hormonal growth factor that stimulates the bone marrow to make platelets. Genetically engineered thrombopoietin (recombinant human thrombopoietin, or rhTPO) recently became available.