P1614: tapering scheme and sustained response in patients with itp treated with fostamatinib

Topic: 32. Platelet disorders Background: Fostamatinib is a splenic tyrosine kinase (SYK) inhibitor, which acts by slowing down the signal transduction of B-lymphocyte receptors and Fc-activating receptors, thereby reducing antibody-mediated platelet destruction. It is an orally administered drug, which has recently been approved in our country for the treatment of adult patients with chronic immune thrombocytopenia (ITP) resistant to other treatments. Aims: There is little information about tapering and sustained remission in patients with ITP treated with fostamatinib. Only individual case reports have been published, we present the case series experience of the GACC (Grupo Andaluz de Coagulopatías Congénitas) from Andalucía, Spain. The objective is to describe the characteristics of the patients in whom it has been performed, tapering method and sustained response rate. Methods: Fostasur is an observational, retrospective, multicenter study whose objective is to evaluate the efficacy and safety of fostamatinib in patients with primary and secondary ITP, older than 18 years. The demographic characteristics of the subjects, response rates and times, need of rescue or combined treatment, tapering and rate of sustained responses, relapses rate and toxicity have been analyzed. The definition of ITP and response criteria are those described by Provan et al. Tapering was performed in subjects who achieved complete response (CR) for at least 6 months, with a progressive reduction of 30% of the weekly dose every 4 weeks if the platelet count remained above 100x10e9/L. Results: A total of 44 patients have been registered in 12 reference centers between October 2021 and February 2023. Table 1 describes the overall characteristics of the global series and patients in whom tapering has been performed. With a median follow-up from the start of fostamatinib of 8 months (IQR: 5-11), tapering has been achieved in 22.7% (10/44) of the subjects, discontinuing the drug in 50% of them (5/10). In subjects achieving drug discontinuation, median time from treatment initiation to response is 3 weeks (IQR:1.3-4), time to CR 4 weeks (IQR:2.5-4), time to start tapering of 16 weeks (IQR: 3-20), duration of tapering 23 weeks (IQR: 14-28). Median platelet count at tapering was 276x10e9/L (IQR:230-343x10e9/L) and at discontinuation 241x10e9/L (IQR:175-360x10e9/L). With a median follow-up since discontinuation of 11 weeks (range: 3-22), only one patient has relapsed at week 11 after discontinuation. At relapse, patient presented platelets of 10x10e9/L and relapse was not related to any concomitant event. Fostamatinib was restarted at a dose of 100mg/12 hours, achieving a new CR in 3 weeks without rescue or concomitant treatment. No getting CR, Chronic ITP and need of rescue treatment are negative predictive factors for tapering and discontinuation. Summary/Conclusion: Fostamatinib is a safe and effective drug in the treatment of ITP. In our experience, the sustained response rate at 3 months is 11%. We found not getting CR, chronic ITP and needs of rescue treatment are negative predictive factors to get tapering and no predictors of sustained response. We found no other significant factors, maybe because of the short number of patients, but non chronic ITP and non-refractoriness to thrombopoietin analogues could be related with sustained response. Table 1. Serie characteristicsKeywords: SYK, relapsed/refractory, Idiopathic thombocytopenic purpura (ITP)