Safety of Romiplostim (Nplate®) Following UCBT

Inclusion Criteria: * Any patient who has undergone a single or double umbilical cord blood transplant (UCBT) except those with primary myelofibrosis. * Those with acute leukemia must be in remission at the time of transplant * Must have achieved neutrophil engraftment (defined as an ANC \>500 for three consecutive days) and be off daily G-CSF prior to starting romiplostim. Intermittent G-CSF is allowed. * Failure to achieve platelet engraftment (defined as platelet count ≥20x10\^9/L on 3 consecutive measurements without transfusion for 7 days) by day +28 post UCBT * Between day +28 and day +42 status post myeloablative or nonmyeloablative UCBT (single or double cord blood transplant) * Age ≥ 18 years * Adequate organ function within 7 days of enrollment defined as: * Creatinine: ≤ 2.0 mg/dL * Hepatic: SGOT and SGPT \< 5 x upper limit of institutional normal (ULN) * Women of child bearing potential agree to use effective contraception during therapy and for 4 months after completion of therapy * Voluntary written consent Exclusion Criteria: * Known pregnancy - Pregnancy Category C: there are no adequate and well-controlled studies of romiplostim in pregnancy * Recurrence of AML or myelodysplastic syndrome on bone marrow evaluation done within 21 days of enrollment * Presence of clinically significant bone marrow fibrosis on the bone marrow examination immediately prior to UCBT * Patients requiring more than one platelet transfusion per day * History of an allergy to romiplostim