Molecular Monitoring of Response to Imatinib (Glivec) in Chronic Myeloid Leukemia Patients: Experience at a Tertiary Care Hospital in Saudi Arabia

Aim: The aim of this study was to evaluate the response and resistance of cases to chronic myeloid leukemia (CML) therapy with tyrosine kinase (TK) inhibitors (imatinib mesylate) and to search for mutations in the breakpoint cluster region (BCR)-Abelson murine leukemia (ABL) kinase domain prior to and during therapy. Methods: Molecular response was assessed with real-time quantitative reverse transcription-polymerase chain reaction and was expressed as the ratio between BCR-ABL and ABL (k562 cell line) x 100. In addition, we searched for mutations in BCR-ABL kinase domain by amplification and direct sequencing of cDNA products of archived RNA samples. Results: There were 85 cases of CML Philadelphia-chromosome-positive patients. Measles, mumps and rubella (MMR) of 0.05% was achieved in 40 (47%) of 85 patients and 3-log reduction was achieved in 37 (44%) after 6 months of imatinib therapy. When molecular monitoring was extended to 12 months in a subset of delayed responsive cases (17 cases) who did not achieve an MMR at 6 months, significant changes in BCR-ABL/ABL ratio were noticed. Fifteen de novo CML patients were started directly on treatment and were monitored for BCR-ABL/ABL ratio for a further period of up to 24 months. Their median of BCR-ABL/ABL ratio was 18% at diagnosis, 0.3% after 6 months, 0.2% after 12 months, and 0.01% after 18 and 24 months. Four (27%) of 15 patients achieved MMR as 3-log reduction after 6 months, 6 (40%) after 12 months, 9 (60%) after 18 months, and 7 (46%) after 24 months. No mutation(s) or polymorphism(s) were detected in all tested patients at diagnosis, at 6 months following imatinib and following 12 months for patients showing delayed response. Conclusion: BCR-ABL mutations are rare in early chronic phase and increases with CML disease progression. Therefore, search for other causes in resistant cases at this phase should be sought.