Low JAK2V617F Allele Burden in Primary Myelofibrosis, Compared to Either a Higher Allele Burden or Unmutated Status, Predicts Inferior Overall and Leukemia-Free Survival.
Authors: Tefferi Ayalew , Lasho Terra L. , Huang Jocelin , Finke Christy , Hanson Curtis A. , Mesa Ruben A. , Pardanani Animesh 
Published: November 2019

Abstract
Background : Two previous studies have reported significant but inconsistent associations between the presence of JAK2V617F in primary myelofibrosis (PMF) and older age at diagnosis, risk of thrombosis, higher leukocyte count, and inferior survival (Tefferi, et al. BJH2005;131:320, Campbell, et al. Blood2006;107:2098). The clinical relevance of V617F allele burden in PMF has not been previously studied.
Methods : Diagnosis of PMF was based on the World Health Organization criteria and study eligibility included the availability of bone marrow-derived DNA that was collected either at time of diagnosis or within one year of diagnosis. Quantitative allele specific PCR was utilized to meaure V617F allele burden.
Results I. V617F-positive vs. V617F-negative comparisons: A total of 199 patients (60% males; median age 61 years) were suitable for analysis of comparisons between mutation-positive and mutation-negative disease. The Dupriez prognostic scoring system (PSS) risk distributions were 61% low-risk, 31% intermediate-risk, and 8% high-risk. Hypercatabolic symptoms were present in 27% of the patients and ≥1% peripheral blood (PB) blasts in 37%. At a median follow-up of 23 months (range 0–266), 57 patients (29%) had died, 17 (9%) developed leukemic transformation (LT) and 10 (5%) experienced major thrombosis. V617F mutational frequency was 58%. Univariate analysis identified older age (p=0.0007), platelet count ≥ 100 x 109/L (p=0.05), and PB blast percentage < 3% (p=0.001) as being associated with a positive mutational status; all three variables sustained their significance during multivariable analysis. The presence of the mutation did not affect the incidence of thrombosis (p=0.78), overall survival (p=0.22) or leukemia-free survival (p=0.5).
Results II. Clinical correlates of V617F allele burden: Quantitative measurement of V617F allele burden was performed in 129 patients that were divided into four groups: V617F-negative (n=53) and V617F-positive with mutant allele burden in the lower quartile (n=19), middle quartiles (n=38), or upper quartile (n=19) range (median and range of V617F allele burden ratio was 29% and 1% to 74%). Kaplan-Meier plots revealed significantly shortened overall (Figure; p = 0.0008) and leukemia-free (p = 0.01) survival for the lower quartile allele burden group; survival significance was sustained in a multivariable analysis that included the Dupriez PSS. Lower quartile allele burden was also associated with lower leukocyte count (p = 0.003) and presence of hypercatabolic symptoms (p=0.05). Thrombosis incidence was not affected by allele burden.
Conclusions: In PMF, patients with a low V617F allele burden, compared to those with either undetectable (i.e. wild-type) or higher allele burden, display significantly shorter overall and leukemia-free survival. In contrast, the presence or absence of the mutation, by itself, does not result in distinct groups that differ significantly in terms of survival, LT, or incidence of thrombosis. These data suggest that a low V617F allele burden in PMF is a surrogate for the development of dominant V617F-negative subclones that are more likely to undergo LT.
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