Frequency of coexistence and kinetics of the BCR-ABL1 transcript level and allele burden of JAK2V617F and CALR Type 1, 2 gene mutations in patients with chronic myeloid leukemia

Abstract

Introduction. The pathogenesis of myeloproliferative neoplasms is associated with the chimeric gene BCR-ABL1 or with one of the driver mutations in the genes JAK2, MPL and CALR (Calreticulin). However, the classifi cation of the World Health Organization lists no myeloid neoplasms with more than one driver genetic abnormality. Aim. To search for mutations in the genes JAK2, MPL and CALR in patients with BCR-ABL1-positive chronic myeloid leukemia (CML), as well as to evaluate the kinetics of the discovered mutations during tyrosine kinase inhibitor (TKI) therapy. Materials and methods. mRNA and DNA samples isolated from blood and bone marrow cells of 567 CML patients, who underwent periodic monitoring of the BCR-ABL1 transcript level over the 2012–2019 period were included in the study The BCR-ABL1 transcript level was determined using a highly sensitive quantitative real-time polymerase chain reaction. The mutations JAK2V617F and MPLW515L/K were detected using real-time quantitative allele-specifi c polymerase chain reaction. Mutations in the CALR gene were investigated using fragment analysis followed by Sanger sequencing. Results. The combination of the BCR-ABL1, JAK2 and CALR gene mutations among CML patients receiving TKIs was 1.23 % (7/567). Out of these, the combination of BCR-ABL1 with JAK2V617F and the combination of BCR-ABL1 with CALR gene mutations were detected in 0.88 % (5/567) and 0.35 % (2/567) of cases, respectively. During TKI therapy, in 5 out of 7 patients, the level of BCR-ABL1 reached major molecular response (MR). In 4 of these patients, the therapy was discontinued. These patients are currently in molecular remission. In the remaining 2 patients, major MR was not achieved, despite the use of second-generation TKI preparations. Conclusions. The combination of the BCR-ABL1 chimeric gene with gene mutations Jak2 or CALR was a rare event and amounted to 0.88 and 0.35 % of cases, respectively. The combination of BCR-ABL1 with Jak2V617F and CALR mutations does not always impede the achievement of major MR.