Thrombocytosis in Myelodysplastic Syndromes: Not an Innocent Bystander

Background: 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 is to determine if thrombocytosis predicts Overall Survival (OS). Methods: We reviewed a prospective cohort of patients with myeloid disorders from 1994 to July 2011. The median duration of observation was 6.3 years. The cohort included 5,886 bone marrow biopsies or aspirates from 2,042 patients. OS of patients with thrombocytosis was compared to WHO case matched patients with normal (100-450,000) and low platelet counts (<100,000). All-cause mortality was evaluated using Cox proportional hazard regression modeling and Kaplan Meier methods. Results: Thrombocytosis occurred in 5% (102/2,042) of patients throughout their disease. Platelet counts remained stable in 86% of patients (1,593/1,856) and thrombocytosis was constant in 93% of patients (86/92). Patients with thrombocytosis had significantly decreased OS compared to those with normal platelet counts in multivariate analysis adjusted for age and IPSS score (P< 0.035). Patients with normal platelet counts had the best prognosis and patients whose platelet counts changed during their disease course had the worst survival (p< 0.0009). Conclusions: MDS patients with thrombocytosis have significantly decreased OS compared to those with normal platelet counts. The IPSS score does not accurately predict their prognosis. The purpose of this study is to define the incidence of thrombocytosis in MDS and determine its prognostic impact on overall survival.