Spectrum of BCR-ABL Kinase Domain Mutations; A Cohort Study from Saudi Arabia

Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasm (MPN) associated with a characteristic translocation between chromosome 9 and 22 to form Philadelphia chromosome (Ph). The introduction of tyrosine kinase inhibitors (TKIs) imatinib for CML marked a new era for targeted therapy. In general CML patients in chronic phase (CP) have a very good response to Imatinib with a ~85% projected overall rate of survival. However, a significant proportion harbor molecular residual disease and develop acquired resistance after initial response through a number of cellular and molecular mechanisms in which mutations in the Abl kinase domain are the best known cause of resistance. Mutations are detected in 35% of patients with resistance to TKI in Chronic Phase and up to 80% in patients with accelerated phase and blast phase.

Given the clinical importance of the mutation status, mutation analysis was established as a clinical service to aid in the clinical decision and identify the subset who would benefit from alternative therapies.

In this retrospective study, we assessed the ABL kinase domain mutation in 93 patients referred from our clinics at King Faisal Specialist Hospital and Research centre (General Organization) between 2011-2013 with Ph positive CML displaying either refractory to TKI or resistance displaying increase BCR-ABL1 levels by serial monitoring using Quantitative PCR. Mutation analysis was performed on RNA extracted from either blood or Bone marrows after amplification of the BCR/ABL1 transcript by nested PCR followed by Direct sequencing of the BCR-ABL1 Kinase domain including residues 243-487.

In total, 93 patients (46 Females and 47 males), Age between 10-71 years (median age: 38 years) of which 89 were adults and 4 pediatrics were analyzed. Among 93 patients, 20 (21.5%) were positive for 10 different mutations across the ABL1 Kinase domain mutations (7 patients had T315I, 3 patients had each of the following mutation: Y253H, F359I, 2 patients with E255K. Additionally, one patient with each of the following mutations: E355G, V299L, L248V, L298, Y326H and F317L). The duration from diagnosis to mutation detection ranged between 3-144 months with a median duration of 4 years.

Despite the retrospective nature and the relatively small sample size of a single center analysis, the mutation frequency is in line with similar studies reported from our region.

Further follow up is needed to identify the outcome of these patients acquiring ABL kinase mutations on targeted therapy.