Frequency, Distribution and Prognostic Value of ABL Kinase Domain (KD) Mutations in Different Subsets of Philadelphia-Positive (Ph+) Patients (Pts) Resistant to Imatinib (IM) by the Gimema Working Party on CML.

Using denaturing-high performance liquid chromatography and sequencing, we screened for ABL KD mutations 319 IM-resistant Ph+ pts. Median time between diagnosis and IM start at 400–600 mg/d was 40 (0–160) months. Median duration of IM was 27 (9–62) months. Evaluable pts were 256/319 (80%). At the time of analysis, 178/256 (70%) pts were in chronic phase (CP)(36 previously untreated, 142 post-IFN failure), 16 (6%) pts were in accelerated phase (AP), 26 (10%) pts were in myeloid blast crisis (myBC), 36 (14%) were in lymphoid blast crisis (lyBC) or had Ph+ acute lymphoblastic leukemia (ALL). One hundred and forty-two pts had primary resistance to IM, 114 had acquired resistance. Ninety-eight mutations were found in 91/256 (36%) pts. In 6 pts (2 Ph+ ALL, 2myBC, 1 lyBC, 1 CP post-IFN failure) multiple mutations simultaneously occurred. Mutations mapped to 15 codons, the most frequent ones being E255K/V (15 pts), Y253F/H (12 pts), T315I (10 pts), M351T (10 pts), F359V/I (10 pts), M244V (9 pts), G250E (8 pts). Three novel amino acid substitutions (F311I; E355D; F359I) and a novel mutated codon (P296H) were detected; biochemical/structural characterization will be presented. Mutations were found in 36/178 (26%) CP pts (4/36 (11%) previously untreated, 32/142 (22%) post-IFN failure), 7/16 (44%) AP pts, 19/26 (73%) myBC pts and 29/36 (81%) lyBC/Ph+ ALL pts (CP vs. AP, p=.04; AP vs. BC, p=.01; CP vs. BC, p<.001). Mutations were associated in 41/142 (29%) pts with primary resistance (4/8 hematologic and 37/134 cytogenetic) and in 50/114 (44%) pts with acquired resistance (10/50 pts who lost CCgR, 16/32 pts who lost HR, 24/32 pts who progressed to AP/BC)(primary vs. acquired, p=.009). Thirty-nine out of 49 pts with P-loop or T315I mutations had already progressed to AP/BC at the time of mutation detection; 4 additional pts subsequently progressed. In contrast, only 17 of the 42 remaining pts with mutations had progressed or subsequently progressed (p<.001). In a subset of 93 IM-resistant CP pts who were homogeneously treated in the CML/002/STI571 trial, with a follow-up ranging between 10 and 51 months, presence of a mutation was significantly associated with greater likelihood of progression (Log-Rank p<.001) and shorter survival (Log-Rank p=.005). Pts carrying P-loop or T315I mutations showed a particularly poor outcome both in terms of time to progression (Log-Rank p=.003) and in terms of survival (Log-Rank p=.02). We conclude that: a) there is a significantly higher probability of mutations according to disease phase (Ph+ ALL and BC>AP>CP); b) there is a significantly higher probability of mutations in pts with acquired resistance vs. pts with primary resistance; c) mutations, and in particular those affecting P-loop or codon 315, are associated with a worse outcome. Supported by AIL, AIRC, Fondazione del Monte di Bologna e Ravenna.