Correlation Of Longitudinal Blood Counts With Thromboembolic Complications In WHO 2008 Defined Prefibrotic Primary Myelofibrosis
Authors: Buxhofer-Ausch Veronika , Schalling Martin , Frantal Sophie , Thiele Jürgen , Muellauer Leonhard , Kvasnicka Hans-Michael , Gisslinger Bettina , Gisslinger Heinz 
Published: October 2019

Abstract
Current treatment strategies in the classical Philadelphia- negative myeloproliferative diseases are challenged by the compelling evidence of the important role of white blood cell (WBC) counts for the risk of thrombosis (Barbui Blood 2013). Moreover, recent publications disclosed significant differences in regards of certain disease characteristics, vascular risk profiles and prognosis between WHO 2008 (Tefferi Blood 2007) classified essential thrombocythemia (ET) and prefibrotic primary myelofibrosis (PMF) (Kvasnicka Am J Hematol 2008; Barbui JCO 2011; Buxhofer-Ausch Am J Hematol 2012). Hence, patients cohorts classified prior to WHO 2008 may likely consist of a mix of patients with ET and prefibrotic PMF. A recent analysis of the prior to WHO 2008 classified UK-PT1 cohort demonstrated, that not blood counts at diagnosis but enhanced longitudinal WBC counts measured during the course of the disease correlate with the risk of vascular complications in ET (Campbell Blood 2012).
The current study aimed to correlate longitudinal blood counts with thromboembolic events in patients from our institution, all reclassified according to WHO 2008 as prefibrotic PMF.
In 76 patients with a valid consensus diagnosis of prefibrotic PMF longitudinal blood counts including hemoglobin levels, WBC counts and platelet counts were collected retrospectively from the patient’s records (most patients were followed every 3-4 months). Subsequently, these parameters along with certain disease specific and laboratory parameters were correlated with the incidence of major arterial or venous thrombosis after diagnosis by applying Cox-regression analyses.
While overtime-platelet counts (mean 553.14±287.04) were significantly lower than baseline platelet counts (mean 806.61±372.51), WBC counts did not change over time (baseline mean 10.60±4.11; over-time mean 10.64±9.2). By correlating 1644 longitudinal blood counts with major venous and/ or arterial thromboembolic events after diagnosis neither a significant correlation of overtime- platelet counts with total thrombosis (p= 0.347) nor with arterial thrombosis (p= 0.516) was seen. In contrast, there was a clear statistical trend for correlation of over-time WBC counts with total thrombosis (p= 0.072) and- even more pronounced- with arterial thrombosis (p= 0.057). Comparison of these data to a cohort of 111 patients with WHO 2008 diagnosed ET will be presented.
In conclusion our data presume an important role of over-time WBC counts on vascular events in patients with prefibrotic PMF. Apparently our current treatment strategies are not sufficient enough to lower WBC counts over- time. Appropriate medication for lowering WBC counts has to be implemented in future treatment concepts. Studies on larger, WHO 2008 diagnosed patient cohorts are needed to confirm and extend this important findings.

Disclosures:
Thiele: AOP Orphan Pharmaceuticals, Incyte, Novartis, Shire, Sanofi: Consultancy; Novartis, Shire: Research Funding; AOP Orphan Pharmaceuticals, Incyte, Novartis, Shire, Sanofi: Honoraria. Gisslinger:AOP Orphan Pharmaceuticals: Advisory Board Meeting Other, Honoraria; Novartis: Advisory Board Meeting, Advisory Board Meeting Other, Honoraria; Sanofi-Aventis: Advisory Board Meeting, Advisory Board Meeting Other, Honoraria; Shire: Advisory Board Meeting, Advisory Board Meeting Other, Honoraria; Celgene: Advisory Board Meeting Other, Honoraria; Janssen: Advisory Board Meeting, Advisory Board Meeting Other, Honoraria.