[Efficacy of fostamatinib add-on for TPO receptor agonist-refractory immune thrombocytopenia]

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by thrombocytopenia caused by platelet destruction and impairment of platelet production by anti-platelet autoantibodies. The Syk inhibitor fostamatinib was approved in Japan in December 2022 for the second-line treatment of chronic ITP. However, data on combination therapy with thrombopoietin receptor agonists (TPO-RAs) remain limited because these regimens have not been investigated in clinical trials. Here we report four cases of relapsed/refractory ITP treated with a combination of fostamatinib and TPO-RAs. Two patients discontinued fostamatinib due to adverse events after starting combination therapy, but all patients showed an increase in platelet count, with one patient achieving corticosteroid discontinuation. Notably, some patients showed a rapid platelet increase, indicating a need for caution regarding thrombotic events. The combination of fostamatinib and TPO-RAs may provide an additive effect due to their distinct mechanisms of action, offering a promising therapeutic option for refractory ITP. As this report includes only a small number of cases, more cases are needed to evaluate the efficacy and safety of this combination.