Detection of BCR-ABL Mutations in Patients with Chronic Myeloid Leukemia Treated with Imatinib. Experience of One Centre.

Abstract Abstract 4280 Introduction Imatinib (Imatinib) offers outstanding results in the treatment of chronic phase of chronic myeloid leukaemia (CML). However, there are still some patients who do not achieve an optimal response. There are several possible mechanisms both for primary refractoriness and for acquired resistance, but very often the blame falls in the appearance of ABL-kinase-domain (KD) mutations. Different mutations are related to variable degrees of resistance, ranging from the extreme refractoriness of the mutation T315I down to some which appear to have no clinical significance. Aims To define the clinical characteristics and outcome of patients treated in our centre, in which ABL-kinase-domain mutations through direct DNA sequencing have been analysed. Results In 24 of a total 86 patients, KD mutations were looked for. Screening for mutations was undertaken for one of three reasons: at diagnosis in 6 patients, suboptimal response (Leukemia-Net criteria) in 10 cases and Treatment-Failure (LN criteria) in 8 cases. Median time from diagnosis to ABL mutation detection was 38 months. No risk factors at diagnosis for the appearance of KD mutations have been found. Of the 7 mutations, 5 cases corresponded to treatment failures and 2 to patients in so-called suboptimal responses. One patient, after achieving a complete response to Imatinib, developed a T315I KD mutation and died due to blastic crisis despite having received second generation TKI. Another patient in failure (mutation G250E) achieved a molecular response with dasatinib. No mutations were found in 6 patients checked before treatment, but one of these developed a mutation G250E after 18 months, along with the criteria of a suboptimal response and achieved a mayor molecular response with dasatinib. Conclusions KD mutations are found in a proportion of patients in the situation of suboptimal response or failure to IM, more frequently in the latter in our experience, but the clinical significance of some of them is still unclear. On the contrary, DNA sequencing for screening at the moment of diagnosis offers little relevance in chronic phase CML. Disclosures: No relevant conflicts of interest to declare.