C085 | PREVALENCE AND CLINICAL IMPACT OF CLONAL HEMATOPOIESIS IN PAROXYSMAL NOCTURNAL HEMOGLOBINURIA: A MULTICENTER STUDY.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic stem cell disorder characterized by complement-mediated intravascular hemolysis, bone marrow failure and thrombosis. Recent insights into its molecular landscape, particularly in cases associated with myelodysplastic syndromes (MDS) or aplastic anemia (AA), have highlighted the role of somatic mutations (i.e. clonal hematopoiesis, CHIP) in disease heterogeneity. We retrospectively analyzed 56 PNH patients across multiple Italian centers to evaluate the prevalence and clinical significance of somatic mutations of myeloid genes other than PIG-A by next-generation sequencing (NGS). Mutations were further stratified according to the presence of high-risk clonal hematopoiesis (HR-CHIP), as per Stonestrom and Weeks. At least one pathogenic or likely pathogenic mutation was found in 17 patients (30%), while 39 (70%) were NGS-negative. ASXL1 was the most common mutation (11 cases), followed by TET2 (3), U2AF1 (3), and RUNX1 (3). Less frequent mutations included DNMT3A, EZH2, ETV6, and others such as JAK2, KDM6A, SETBP1 and CALR. NGS-positive patients were significantly older than NGS-negative ones (median 53 vs 35 years; p=0.05), while gender distribution was similar. CHIP prevalence was higher in patients with classic PNH versus MDS/AA PNH (65% vs 35%, p=0.08). NGS-positive cases also showed non-significant trends toward higher prevalence of thrombosis (35% vs 20%) and larger clone sizes, especially in granulocytes (81% vs 72%) and monocytes (87.2% vs 67.4%). HR-CHIP mutations were found in 11 of the 17 NGS-positive patients (65%). These patients were older (median 55 vs 35 years; p=0.04) and had larger monocyte clone sizes (92.3% vs 67%; p=0.05). Overall, 52% of patients received therapy, mainly complement inhibitors (anti-C5 in 37%, anti-C3 in 3%, and factor B/D inhibitors in 10%), with similar response rates and breakthrough hemolysis events across groups. In conclusion, the prevalence of somatic mutations other than PIG-A among PNH patients was 30%, of whom 65% were HR-CHIP. A higher prevalence was noted in older patients with classic-hemolytic PNH, a larger clone size on monocytes and a trend for higher thrombotic risk, suggesting a possible contribution of additional somatic mutations to PNH clone dynamics.