Development of pancytopenia with neutralizing antibodies to thrombopoietin after multicycle chemotherapy supported by megakaryocyte growth and development factor.

Clinical trials of thrombopoietin (TPO), the central regulator of megakaryocytopoiesis, have revealed few side effects associated with its use. We here report a case of pancytopenia associated with the development of neutralizing antibodies to TPO that occurred in a patient who had undergone multicycle chemotherapy with multiple cycles of subcutaneous administration of pegylated recombinant human megakaryocyte growth and development factor. Samples of the patient's bone marrow showed trilineage hypoplasia with absence of myeloid, erythroid, and megakaryocyte progenitor cells but with elevated endogenous levels of erythropoietin, granulocyte colony-stimulating factor, and stem-cell factor.