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Abl Kinase Domain Mutations in Imatinib-treated Egyptian Patients with Chronic Myeloid Leukemia

Yasser H Elnahass, Hossam K Mahmoud, Fahmy T Ali, Mohamed R Mohamed, Mahmoud M Said, Mohamad Abdel Moaty Samra,Mohamed AM Ali, Amir Salem and Wafaa H ElMetnawy

Background: Point mutations within ABL kinase domain (AKD) of the BCR-ABL gene are the most common cause of resistance to Imatinib Mesylate (IM) treated Chronic Myeloid Leukemia (CML) patients. Objectives: To assess the frequency, type and impact of AKD mutations on prognosis in a cohort of Egyptian CML patients. Patients and methods: Serial measurements of BCR-ABL transcripts level in 175 IM treated CML patients were performed using real time quantitative polymerase chain reaction (RQ-PCR). Mutation screening was performed by allele specific oligonucleotide polymerase chain reaction (ASO-PCR) in 72 patients including all 42 non-optimal responders; 28 resistant patients, 18 suboptimal responders in addition to 30 patients randomly selected with stable/ decreasing transcript level representing an optimal responder category. Results: AKD mutations were detected in 16/28 resistant patients (57%) at time of >2-fold rise in BCR-ABL transcript and in none of the 44 optimal or suboptimal responders (0%) with decreasing or stable transcript levels. From 16 positive patients, P-loop mutations were detected in 9 patients; Q252H in 3 patients (19%), Y253H in 2 patients (12%), Y253F in 2 patients (12%) and E255K in 2 patients (12%). T315I was detected in 1/16 (6%) patient. Regarding non P-loop mutation; V299L was detected in one patient (6%), M351T in 4 patients (25%), F359V in 2 patients (12%). One patient had both Y253H and E255K mutations. Ten/16 (62%) patients carrying mutations experienced disease progression versus 1/56 (2%) in non mutation group (p=0.001). Median progression free survival (PFS) and overall survival (OS) of the mutation group was 13.5 months and 37.5 months, respectively versus 42.6 months in non mutation group (p=0.001). The estimated PFS and OS at 49 months in patients with mutations were 37.5% and 56.3% respectively versus 98.2% in non mutation carriers (p2-folds in IM resistant patients may signal progression that implies testing for AKD mutations and early planning for second generation tyrosine kinase inhibitors (TKIs). P-loop mutations are significantly associated with advanced CML phases and poorer OS than non-P loop mutations. ASOPCR is a valuable tool for detection of mutations in countries where sequencing facilities are not available.