Real-World Clinical Outcomes With Fostamatinib for the Treatment of Refractory Chronic Immune Thrombocytopenia

Presenting Authors: Donald C. Moore, PharmD, BCPS, BCOP, DPLA, FCCP (First Author), Levine Cancer Institute, Atrium Health, Charlotte, NC; Justin Arnall, PharmD, BCOP (Senior Author), Atrium Health Specialty Pharmacy Service, Charlotte, NC

Co-Authors: Joseph B. Elmes, PharmD, BCOP, and Mauricio Pineda-Roman, MD, FACP, Levine Cancer Institute, Atrium Health, Concord, NC

BACKGROUND: Fostamatinib is a spleen tyrosine kinase inhibitor indicated for the treatment of chronic immune thrombocytopenia (ITP) that is unresponsive to at least 1 previous treatment. However, fostamatinib is often reserved for later lines of therapy after prior treatment with corticosteroids, rituximab, and a thrombopoietin receptor agonist. Real-world studies evaluating the utilization and effectiveness of fostamatinib outside the context of a clinical trial are lacking.

OBJECTIVE: To evaluate the effectiveness of fostamatinib for the treatment of ITP in a real-world cohort.

METHODS: We conducted a single-center, retrospective, observational study to evaluate the effectiveness of fostamatinib for the treatment of ITP. Eligible patients included adults aged >18 years who received fostamatinib for previously treated ITP. The primary end point was durable response as defined by the American Society of Hematology ITP response criteria. The secondary end points included overall response rate, time to response, and safety. Subgroup analysis was performed to assess the frequency of durable response in key subgroups of patients based on prior therapies. This study was approved by the institutional review board.

RESULTS: A total of 31 patients treated with fostamatinib for ITP were included in our analysis. Patients had received a median of 4 prior lines of therapy. Most patients had been previously treated with corticosteroids (100%), a thrombopoietin receptor agonist (93%), IVIG (74%), and rituximab (71%). A total of 10 (32%) patients achieved a durable response. Most patients who had a durable response maintained their response at 24 months (n=7; 70%). The median time to response was 9 days. Most patients (n=24; 77%) required a dose adjustment from 100 mg twice daily to 150 mg twice daily. In all, 4 (13%) patients discontinued fostamatinib as a result of an adverse event. The subgroups that had higher rates of durable responses included those who had received 2 or 3 prior lines of therapy (40%), splenectomized patients (50%), and those who had not received prior rituximab (55%).

CONCLUSION: Fostamatinib therapy in a real-world population of patients with heavily pretreated ITP led to the achievement of a durable response in one-third of patients, which was maintained for most responders. There may be specific patient populations and treatment histories for which fostamatinib may elicit the most clinical benefit. In addition, because most patients’ doses were escalated to 150 mg twice daily, this should be evaluated as a potential starting dose for fostamatinib in ITP in the future.

1. Moore DC, Gebru T, Muslimani A. Fostamatinib for the treatment of immune thrombocytopenia in adults. Am J Health Syst Pharm. 2019;76:789-794.
2. Bussel J, Arnold DM, Grossbard E, et al. Fostamatinib for the treatment of adult persistent and chronic immune thrombocytopenia: results of two phase 3, randomized, placebo-controlled trials. Am J Hematol. 2018;93:921-930.
3. Bussel JB, Arnold DM, Boxer MA, et al. Long-term fostamatinib treatment of adults with immune thrombocytopenia during the phase 3 clinical trial program. Am J Hematol. 2019;94:546-553.
4. Boccia R, Cooper N, Ghanima W, et al. Fostamatinib is an effective second-line therapy in patients with immune thrombocytopenia. Br J Haematol. 2020;190:933-938.
5. Hughes D, Blevins F, Shah B, et al. Real-world experience with fostamatinib in patients with immune thrombocytopenia at an academic medical center. Blood. 2019;134(suppl 1):4912.
6. Lee EJ, Izak M, Bussel JB. Long-term sustained response to fostamatinib in two patients with chronic refractory immune thrombocytopenia (ITP). Br J Haematol. 2020;189:379-382.
7. Hughes DM, Toste C, Nelson C, et al. Transitioning from thrombopoietin agonists to the novel SYK inhibitor fostamatinib: a multicenter, real-world case series. J Adv Pract Oncol. 2021;12:508-517.
8. Liu J, Hsia CC. The efficacy and safety of fostamatinib in elderly patients with immune thrombocytopenia: a single-center, real-world case series. Adv Hematol. 2022;2022:8119270.