P1613: real-world use of fostamatinib in france. interim results of a national registry.

Topic: 32. Platelet disorders Background: Fostamatinib, a spleen tyrosine kinase inhibitor, has been marketed in France for the management of adult chronic immune thrombocytopenia (ITP) in October 2021. French authorities recommended the use fostamatinib in case of failure or contraindication to eltrombopag, romiplostim (the two thrombopoietin receptor agonists – TPO-RAs – available in France), rituximab and splenectomy, after validation by a referral center. Aims: To assess the use, the effectiveness and the safety of fostamatinib in adult patients with ITP in the real world in France after one year of availability of the drug. Methods: The source of study population was the French fostamatinib registry, appended to the CARMEN-France registry since fostamatinib marketing in France. The CARMEN-France registry is the registry of the French referral network for autoimmune cytopenias, that prospectively includes adult patients with a new diagnosis of ITP. Adult patients were included in the fostamatinib registry 1) if they were previously included in the CARMEN-France registry and started fostamatinib or 2) if they were not already in the registry but initiated fostamatinib. In that latter case, a retrospective assessment of ITP history was recorded. Patients who initiated fostamatinib between October 2021 and October 2022 were selected in the present interim analysis. We described the patients’ characteristics, the duration of exposure to fostamatinib, the achievement of response (platelet count ≥30 × 109/L with no other concomitant treatment), the withdrawal of concomitant ITP treatment at fostamatinib initiation, the need of treatment rescue, fostamatinib discontinuation and adverse drug reactions (ADRs, reported by investigators, with a World Health Organization causality score at least as “possible”). Results: Sixty-one patients were prospectively included. Mean age at ITP diagnosis was 51.3 years; 36 (59.1%) were women; 21 (37.8%) had ≥1 comorbidity of the Charlson Comorbidity Index; 14 (23.0%) had chronic arterial hypertension. At ITP diagnosis, the median platelet count was 10 x 109/L and 29 (47.5%) patients had bleeding. Six patients had secondary ITP. Median ITP duration was 6.5 years. The median number of previous exposures to ITP treatments was 5; 86.9% of patients had been exposed to TPO-RA, 86.9% to rituximab and 37.7% were splenectomized. Thirty-seven (61.7%) had a concomitant exposure to another ITP treatment at fostamatinib initiation. The median duration of exposure to fostamatinib at the time of data extraction was 2.2 months. Out of 50 patients with assessable data, 15 (30.0%) had a response without any concomitant ITP medication (8/26, i.e. 30.8% in patients with a duration of fostamatinib ≥12 weeks). A concomitant exposure to corticosteroids at fostamatinib initiation was withdrawn in 4/18 patients, to intravenous immunoglobulin (IVIg) in 2/7 patients and to TPO-RAs in 13/25. Twenty-six (42.6%) patients had at least one rescue treatment. Twenty-eight patients (45.9%) stopped fostamatinib, including 10 for ineffectiveness (only 1 had an exposure <12 weeks) and 12 for ADR. Thirty-two ADRs were reported in 24 (32.4%) patients, mostly diarrhea (n=6) and arterial hypertension (n=6). One thrombosis and 6 infections in 4 patients were reported (not considered as ADRs; all had other risk factors of thrombosis/infections). Summary/Conclusion: Fostamatinib was used in previously very heavily treated patients. One third of patients had ADRs but generally not serious, and >50% of patients were still treated with fostamatinib at the time of the analysis. Keywords: Real world data, Immune thrombocytopenia (ITP)