C010 | INVESTIGATING DISTINCT FEATURES OF PRIMARY IMMUNE THROMBOCYTOPENIA (ITP) REQUIRING TREATMENT ASSOCIATED WITH ANTIPHOSPHOLIPID ANTIBODIES: A SUB-ANALYSIS OF THE ITALIAN ITP REGISTRY (GIMEMA ITP0918)

Introduction. The clinical significance of positive antiphospholipid antibodies (aPL) in patients with primary immune thrombocytopenia (pITP) remains uncertain. To address this gap, we have compared the clinical characteristics of pITP patients with and without aPL positivity. Methods. All patients were identified from the Italian ITP Registry, a retro-prospective multicenter study of adult patients with pITP on active treatment at the time of inclusion. The aPL profile was described in accordance with the 2023 ACR/EULAR criteria. Patients with any aPL positivity were classified as aPL-positive, whereas only those with confirmed triple-negative aPL status were considered aPL-negative. Registry patients with no prior aPL testing or missing data were excluded from the analysis. The primary outcome was the proportion of patients with failure to first-line therapy, defined as the need for any second-line treatment. Other relevant outcomes included pregnancy complications and thrombotic events, including only thromboses occurring after ITP diagnosis and no more than 3 years before the first documented aPL-positivity. The study is sponsored by the GIMEMA Foundation. Data collection and analysis are performed by the Hematology Project Foundation. Results. On April 8^th, 2025, 409 patients were eligible for inclusion (116 aPL-positive and 293 aPL-negative). Among aPL-positive patients, 82 had a single aPL positivity, 18 a double positivity and 16 a triple positivity. Baseline demographics, cardiovascular risk factors, platelet count at baseline visit and ITP phase at baseline were well-balanced, with no statistically significant differences between the groups. The median number of ITP treatments was 2 (IQR 2-3) for both groups (p=n.s.). The proportion of patients with failure to first-line therapy was 80.4% among aPL-positive patients and 79.8% among aPL-negative patients (p=n.s.). The proportion of female patients with pregnancy complications was low and comparable between the groups. There was a higher proportion of aPL-positive patients with eligible thrombotic events compared to aPL-negative patients (17.3% vs 10.5%), although this difference was not statistically significant (p=n.s.). Conclusions. In this preliminary sub-analysis of 409 patients from the Italian ITP Registry, aPL positivity was not associated with distinct features of response to treatment. The trend toward more thrombotic events in aPL-positive patients deserves further investigation.