PF666 LOW JAK2 V617F ALLELE BURDEN PHI‐NEGATIVE CHRONIC MYELOPROLIFERATIVE NEOPLASMS MAY ASSOCIATE WITH ADDITIONAL CALR OR MPL MUTATIONS

Abstract

Background:Jak2 (Janus kinase 2) V617F, CALR (Calreticulin) exon 9 and MPL (receptor for thrombopoietin) exon 10 mutations are associated with the vast majority of Phi‐negative chronic myeloproliferative neoplasms (MPNs). These mutations affect sequential stages of prolipherative signal transduction and therefore after the emergence of one type of mutation another types basically should not have any selective advantages for clonal expansion. However simultaneous findings of these mutations have been reported by different investigators in up to 10% of MPN cases.Aims:To analyze cases with combined mutations in Russian cohort of MPN patientsMethods:Study includes 3267 samples, directed for genetic analysis to the National Research Center for Hematology between 2014 and 2019 from the patients with clinical evidence of MPN. DNAs and RNAs were extracted from blood using reagent kit from Interlabservice (Russia). Jak2 V617F mutation was quantitated by real‐time PCR kit from Syntol (Russia) according to manufacturers instructions. CALR exon 9 deletions/insertions were analyzed by fragment analysis (sensitivity > = 3%). MPL W515L/K mutations were assessed by in‐house allele specific PCR. All cases were tested for phi‐negativity using BCR‐ABl p210 PCR kit from Interlabservice (Russia).Results:In 406 of 3267 cases (12.5%) CALR mutations were detected. In 24 of these 406 cases (6%) Jak2 V617F mutation was found in addition to CALR mutation. Matched measures were obtained at least twice at different time points during the course of disease for these cases. In 19 from 24 (80%) cases with combined CALR and Jak2 mutations V617F allele burden was lower than 3%. Also combination of Jak2 V617F with MPL W515L/K was observed in 3 out of 3267 cases only. Two of them had V617F allele burden lower than 3% (Tabl.1).Summary/Conclusion:Additional mutations may coexist over low background of JAK2 V617F allele. Therefore cases of MPNs with low initial JAK2 V617F allele should be further tested for CALR (and possibly MPL) mutations to ensure correct disease and treatment monitoring. Further dynamic observation studies are required to assess the value of additional mutations for MPN disease progression and treatment outcome.image