Extension Study (Extended Access) of Syk-inhibition Using Fostamatinib to Treat Posttransplant Immune-mediated Cytopenias

Study Description: This is an extension trial of a phase II study which is designed to evaluate the long-term safety and efficacy of fostamatinib in the treatment of post-transplant cytopenias as assessed by hematologic improvement in anemia and/or thrombocytopenia following an additional 12-84 weeks of treatment on the initial phase II trial. The subjects who are deemed responders to the initial 12-week treatment, will be candidates to enroll onto the extension trial for up to 2 years of treatment. Objectives: The primary objective is to evaluate the efficacy for the use of fostamatinib in subjects with post-transplant anemia and/or thrombocytopenia at the end of total 24 weeks of treatment. The secondary objectives are to evaluate the long-term efficacy of subjects on fostamatinib while weaning off fostamatinib treatment either partially or completely. Endpoints: The primary endpoint is: -Proportion of subjects who are able to maintain hematologic recovery (as defined below) by the end of 12 weeks on the extended access trial (total of 24 weeks fostamatinib treatment). Hematologic recovery is defined as: -Hemoglobin \>= 10 g/dL (or at least \>= 2 g/dL above baseline) in subjects enrolled with posttransplant anemia. In subjects with symptomatic anemia, a hemoglobin increase of at least \>= 2 g/dL above baseline is required OR -Platelets \>= 50 X 10\^9/L (or at least \>= 20 X 10\^9/L above baseline) in subjects enrolled with posttransplant thrombocytopenia OR -Both of the above criteria in subjects with posttransplant Evans syndrome The secondary endpoints: * Proportion of subjects who are able to taper off fostamatinib by \>33% while maintaining hematologic recovery as outlined above at the end of the treatment. * Proportion of subjects who are able to completely taper off fostamatinib while maintaining hematologic recovery as outlined above at the end of the treatment. * Change in corticosteroid dose in the total 24 weeks on fostamatinib, measured by median daily weight-based prednisone-equivalent corticosteroid dose in a week, from week 1 to week 24 * Change in the dose of other immunosuppressive agents in the total 24 weeks on fostamatinib, measured by median daily dose of the immunosuppressant in a week, from week 1 to week 24