Sustained response off therapy after fostamatinib: A chronic refractory ITP case report

Fostamatinib is a SYK-inhibitor drug recently approved by the FDA and EMA for treating chronic immune thrombocytopenia. This drug induces a response in about 40% of patients and has a good toxicity profile. It is known that discontinuing thrombopoietin receptor agonists (TRAs) with the maintenance of sustained response off therapy is possible. On fostamatinib, we do not yet have such information. In this case report, we describe the story of a woman with a multirefractory immune thrombocytopenia (steroids, splenectomy, rituximab, both available TRAs). After 16 years from diagnosis, she started fostamatinib therapy within a clinical trial and achieved a complete response. Grade 1-2 headache and diarrhea occurred during the first months of therapy. These adverse events were resolved with dose reduction of fostamatinib. Despite the dose reduction, the platelet count remained steadily above 80 × 109/L. After 4 years, fostamatinib was gradually reduced and finally discontinued with no drop in platelet count. This is the first case in which fostamatinib discontinuation resulted in a sustained response off therapy.

 

Comments：

Fostamatinib is a SYK-inhibitor drug approved by the FDA and EMA for treating chronic immune thrombocytopenia. It is known to induce a response in about 40% of patients and has a good toxicity profile. However, until now, there has been no information available on whether discontinuing fostamatinib would result in a sustained response off therapy.

This case report provides important evidence that fostamatinib discontinuation can result in a sustained response off therapy, similar to discontinuing thrombopoietin receptor agonists (TRAs) with the maintenance of sustained response off therapy. It is essential to note that the patient had been on fostamatinib therapy for four years before discontinuing it, and her platelet count remained steady above 80 × 109/L throughout this time.

The adverse events experienced by the patient, such as grade 1-2 headache and diarrhea, were resolved with a dose reduction of fostamatinib. This highlights the importance of monitoring patients closely for adverse events and adjusting the dose as necessary to maintain the best possible clinical outcome.

Overall, this case report provides valuable insights into the use of fostamatinib in chronic immune thrombocytopenia and the possibility of sustained response off therapy after discontinuation. However, it is essential to conduct further studies to confirm these findings and determine the optimal duration of fostamatinib therapy before considering discontinuation.

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S2625	Fostamatinib (R788)	Fostamatinib (R788), a prodrug of the active metabolite R406, is a Syk inhibitor with IC50 of 41 nM, strongly inhibits Syk but not Lyn, 5-fold less potent to Flt3. Phase 3.

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Syk