Thrombopoiesis-stimulating agents and myelodysplastic syndromes

Thrombocytopenia in patients with myelodysplastic syndromes (MDS) is a frequent cause of haemorrhage-related morbidity and mortality, and is associated with increased risk of leukaemic transformation and reduced overall survival. In addition, thrombocytopenia in MDS limits the tolerability and therapeutic efficacy of disease-modifying therapies, such as azacitidine or lenalidomide. The recombinant human erythropoietin (rHuEPO) erythropoiesis-stimulating agents, epoetin and darbepoetin, are an established component of anaemia management in lower-risk MDS. Their success has, in turn, driven the development of haematopoietic growth factors targeting thrombocytopenia. While recombinant thrombopoietin (THPO) proved too immunogenic for clinical use, novel thrombopoiesis-stimulating agents (TSAs) have the potential to reduce bleeding events, decrease dependency on platelet transfusions and extend exposure to disease-modifying therapies. Two TSAs, eltrombopag and romiplostim, have demonstrated benefit in chronic immune thrombocytopenia purpura (ITP) and safety and efficacy data for use of these agents in MDS is growing. However, important safety concerns remain, such as the potential for stimulation of neoplastic myeloid clones by THPO agonists. In this narrative review, we discuss the rationale and biological mechanism for TSAs in MDS, describe the agents currently available and their mechanism of action, and present current clinical data relating to TSA safety and efficacy in the context of MDS.