The Clinical and Biologic Significance of Thrombocytosis in Myeloid Disorders

Abstract 5031 Purpose Myelodysplastic syndromes (MDS) are typically characterized by peripheral blood cytopenias. However, some MDS is associated with thrombocytosis rather than thrombocytopenia. The prognostic significance of thrombocytosis is unknown. The purpose of this study was to compare the overall survival (OS) of MDS patient based on their platelet count. Methods We reviewed a prospective cohort of patients with myeloid disorders from 1994 to present. Out of the 1,654 unique patients, 102 had platelets > 450,000 (5.7%) throughout their disease; 88 had stable platelet counts, 6 had varying platelet counts, and 12 were excluded because of missing information. OS of patients with thrombocytosis (>450,000 platelet count) was compared to FAB/WHO case matched patients with normal (100–450 platelet counts) and low platelet counts ( Results The worst OS occurred in patients with unstable platelet counts, followed by thrombocytopenia, and then thrombocytosis. Thrombocytopenia was associated with a poorer prognosis than thrombocytosis, although not significantly worse. Patients with normal platelet counts had the best prognosis. Thrombocytosis significantly reduced OS compared to patients with normal platelet counts (HR 1.44, p= 0.04) using adjusted Cox analysis. Thrombocytopenia had significantly reduced OS compared to patient with normal platelet counts (HR 1.8, p=0.0002) using unadjusted Cox regression. Patients who had unstable platelet counts had significantly the worst OS (HR 5.7, p= 0.0009). Both older age at diagnosis and IPSS independently and significantly affected OS. Conclusion MDS patients with both thrombocytopenia and thrombocytosis have significantly decreased OS compared to normal platelet counts.{abspict} Disclosures: No relevant conflicts of interest to declare.