PB1951 THE LANDSCAPE OF BCR-ABL MUTATIONS UNDER TYROSINE KINASE INHIBITOR THERAPY IN A SINGLE INSTITUTE
Authors: S.-H. Chien, J.-S. Lin, T.-J.C. Chiou, J.-P. Gau, C.-Y. Liu, P.-M. Chen, Y.-J. Chen, H.-M. Liu
Journal: HemaSphere (2019)

Background: Chronic myeloid leukemia (CML) is a myeloid proliferative neoplasm characterized by a reciprocal t(9;22) (q34;q11) chromosome translocation, resulting in the chimeric BCR-ABL fusion gene. Tyrosine kinase inhibitor (TKI) is an effective therapy for CML by ABL kinase inhibition, while emergent resistance may be caused by mutations in the BCR-ABL gene resulting in amino acid substitution within this kinase domain. These mutations in ABL kinase domain would impair the drug binding, leading to clinical resistance and be identified using direct sequencing. Aims: To identify important mutations relevant to CML progression, we reported a landscape of BCR-ABL mutation occurrences under TKI therapy and analyzed the correlation of quantitative BCR-ABL transcripts and mutations status in a single institute. Methods: This study for CML patients receiving TKI therapies, and we collected patients’ peripheral blood for BCR-ABL mutations analysis as well as transcripts polymerase chain reaction (PCR) quantitation. Patient's blood would be sampled while increasing BCR-ABL transcripts, disease progression, or shifting to another TKI therapy. The nested PCR for the sequenced region of BCR-ABL were applied for sequencing in both forward and reverse directions by using the ABI Prism 310 sequencer. The value of BCR-ABL quantitation calculated as a percentage of BCR were converted into 10-base logarithmic scale. The value of log reduction was generated by reduction in BCR-ABL levels from the standardized base-line. Patients’ age, gender, diagnosis, phase of disease and TKI therapy were reviewed for analysis. Results: A total of 82 patients with 285 samples were collected. 35 patients had BCR-ABL mutation, while 21 of them had ≥2 mutations during follow up. 29 single, 13 multiple and 13 silent mutations were detected, while 38 points as well as 19 frameshift mutations were identified. T315 mutation was the most common mutation among point mutations, followed by V299L and F317L. Intron 8 35-bp insertion is the most frequent in frameshift mutations. Regarding to the analysis for mutations and log reduction, we found patients with BCR-ABL mutations, either single or multiple would have significantly poorer log reduction as compared to those with no mutation. Point mutations rather than frameshift were associated with less log reduction, while T315I, F317L, T315A, and V299L were significantly correlated with poor log reduction. Detail analysis for mutations and log reduction was illustrated on Table 1. N374S, I313 V, W405R and E466G were also associated with low log reduction, but they didn’t achieve significance owning to being detected once onlySummary/Conclusion: We concluded that BCR-ABL mutation would significantly lead to drug resistance, disease progression with poor leg reduction. The amino acid substitution at T315I, F317L, T315A, and V299L accounted for mainly point mutations and loss of major molecular response. T315I remained the most important and common point mutation, leading disease progression and treatment failure. Mutation analysis is an essential strategy for CML patients taking TKI with unfavorable response and it help to determine the next second-line TKI therapy.