PF657 USE OF A NGS MYELOID PANEL TO FIND CLONALITY IN TRIPLE NEGATIVE ESSENTIAL THROMBOCYTHEMIA. IDENTIFICATION OF NEW MUTATIONS IN DRIVER GENES

Abstract

Background:Essential Thrombocythemia is a clonal haematopoietic stem cell disorder characterized by hypercellularity of the bone marrow with effective haematopoietic maturation and increased numbers of platelets in the peripheral blood. Although more than 90% of the cases present typical mutations in JAK2, MPL and CALR, the remaining cases can become a diagnostic challenge as it requires the presence of a clonal marker or the absence of evidence for reactive thrombocytosis.Aims:To evaluate the use of a Myeloid Panel for the identification of clonal markers in TN ET cases and try to identify new mutations and prognostic determinants in these patients.Methods:A cohort of 32 ET negative for JAK2 V617F mutation (RT‐PCR), CALR canonic mutations (GENESCAN) and MPL W515K and W515L mutations (RT‐PCR) was selected. Average age at diagnosis was 49,08 (range 14–88). Male:Female ratio was 11:21. Average Haemoglobin, leukocytes and platelets at diagnosis were 14.14 g/dl 8,93 x109/L and 820x109/L, respectively. We performed targeted gene sequencing by NGS (Ion Torrent S5XL System–Thermofisher Scientific) using a panel of 33 (before March 2018) or 43 genes (after March 2018) implicated in leukemia prognosis.Results:With a median follow‐up of 5 years (range 0,02–25,43) 2 patients suffered transformation to acute myeloid leukemia, 1 progression to myelofibrosis and 1 presented with suffered a thrombotic event after diagnosis. We found clonality markers in 19 (59%) out of 32 patients. These presented an average of 1,84 (range 1–3) and 1,68 (range 1–3) mutations and mutated genes, respectively. 6 patients (31,57%) presented mutations in driver genes (JAK2, MPL and CALR). Three of them, family, presented with JAK2 R683G, a mutation previously described in acute lymphoblastic leukemia but not in myeloproliferative neoplasms. Other patient had JAK2 L393 V mutation, of undetermined significance and reported in population databases. Another presented the previously described MPL S505C and W515R mutations. Finally, we identified a new deletion in CALR exon 9 (c.1153_1155delAAG, p.K385del). 17 (89,47%) mutated patients presented mutations in non driver genes. Among those the most frequently mutated ones were TET2 (29%), ETV6 (17,6%), SF3B1 and KMT2A (both 11,7%). We found one mutation in VHL, DNMT3A, WT1, TP53, EPAS, CBL, IDH1, TPHO, KIT, ASXL1, EPOR and KRAS.Summary/Conclusion:Triple Negative TE suppose a diagnostic challenge. Here we show that targeted gene sequencing by a myeloid panel is able to identify clonality in up to 59% of the cases. Also, we have described new mutations in driver genes, gaining knowledge on TE molecular basis. Finally, larger cohorts of TN ETs are needed to clearly define the determinants and prognostic factors of this disease.