JAK2V617F Mutation Persists IN Blasts and Mature CELLS of Transformed- JAK2V617F-POSITIVE-MYELOPROLIFERATIVE Neoplasia: A European LEUKEMIA NET (ENL) STUDY
Authors: Rinaldi Ciro R , Rinaldi Paola , Alagia Adele , Gemei Marica , Del Vecchio Luigi , Martino Bruno , Specchia Giorgina , Candoni Anna , Gugliotta Luigi , Vannucchi Alessandro M. , Barbui Tiziano , Pane Fabrizio 
Published: October 2019

Abstract
Abstract 4090
Transformation to acute myeloid leukemia (AML) is a known complication of MPN but the role of JAK2V617F mutation is still undefined. In 2006, Campbell described a possible model for the development of a JAK2WT-AML in a patient with JAK2V617F-MPN and more recently, Theocharides et al. reported that in up to 53% of the patients who developed secondary AML from a JAK2-mutated MPN the mutation was no longer detectable; however the results obtained with DNA extracted from cells scraped or laser-capture-microdissected from bone marrow (BM) or peripheral blood (PB) smears, were confirmed in fresh samples only in few cases. In this study, we collected, by cell sorting, blast cells and mature myeloid cells (granulocytes, GRA) from whole BM aspirates of 40 newly diagnosed patients with AML secondary to MPN (18 derived from PMF; 13 from PV and 9 from ET) and analyzed the JAK2 status before and after leukemic transformation in selected cell compartments. To evaluate the modification in the JAK2 status before and during leukemic transformation we performed ASO-PCR and (QRT)-PCR assay on total BM of the MPN phase and sorted cell populations from AML phase. At the time of MPN diagnosis, JAK2V617F was detectable in 28 of 40 patients (70%) (10 of 18 PMF; 12 of 13 PV and 6 of 9 ET). No cytogenetic abnormalities or MPL and JAK2-exone 12 mutations were detected at this stage. Median time to AML progression (TTP) was 5.09 years (yrs) (range 0.38 – 27.81). A significant difference (p= 0.02) in TTP was found grouping patients according to JAK2 status during the MPN phase [JAK2WT-MPN n=12, TTP median 15.10 yrs (0.38-16.32); JAK2 mutated-MPN n=28, TTP median 4.07 yrs (0.67-27.81)]. Eight patients showed additional abnormalities involving chromosomes 1, 5, 7, 8, 9, 12, 14, 17 and 20 while no other AML-associated mutations (FLT3, NPM, CEBPA, RUNX1) were detectable at this stage. In our cohort of patients we found that JAK2V617F mutation was still present at the blast transformation in both compartments: CD34+ cells (blasts) and CD15+ cells (GRA) in 24 of 28 JAK2 mutated MPN (86%). Four of 28 patients (14%) developed JAK2V617F negative AML starting from a mutated PV with a mean TTP of 5.14 yrs. Interestingly, the WT status was confirmed in blast cells but also in GRA. Surprisingly we found 2 cases of JAK2V617F mutated AML transforming from a WT-PMF. Also in this case the JAK2V617F positivity in the AML phase occurred in both GRA and blast compartments. No differences (p= 0.3) in the allele burden were found comparing MNCs from chronic phase with MNCs of leukemic transformations or comparing GRA with blasts in AML phase. In conclusion, these results contrast with the previous study in which the JAK2 mutation was lost in 53% of blasts during leukemia transformation. In our work, the loss of JAK2V617F mutation during AML progression is a rare event (14%). Additional studies in larger patient series and multivariate analysis are needed before a prognostic role of JAK2V617F mutation regarding time to leukemia transformation can be definitely assessed.

Disclosures:
Vannucchi: Novartis: Consultancy.