title: Sensitive detection of BCR-ABL1 mutations in patients with chronic myeloid leukemia after imatinib resistance is predictive of outcome during subsequent therapy.
abstract: OBJECTIVE
  BCR-ABL1 mutation analysis is recommended to facilitate selection of appropriate therapy for patients with chronic myeloid leukemia after treatment with imatinib has failed, since some frequently occurring mutations confer clinical resistance to nilotinib and/or dasatinib. However, mutations could be present below the detection limit of conventional direct sequencing. We developed a sensitive, multiplexed mass spectrometry assay (detection limit, 0.05% to 0.5%) to determine the impact of low-level mutations after imatinib treatment has failed.
  
  
  METHODS
  Mutation status was assessed in 220 patients treated with nilotinib or dasatinib after they experienced resistance to imatinib.
  
  
  RESULTS
  Mutations were detected by sequencing in 128 patients before commencing nilotinib or dasatinib therapy (switchover). In 64 patients, 132 additional low-level mutations were detected by mass spectrometry alone (50 of 132 mutations were resistant to nilotinib and/or dasatinib). When patients received the inhibitor for which the mutation confers resistance, 84% of the low-level resistant mutations rapidly became dominant clones detectable by sequencing, including 11 of 12 T315I mutations. Subsequent complete cytogenetic response rates were lower for patients with resistant mutations at switchover detected by sequencing (0%) or mass spectrometry alone (16%) compared with patients with other mutations or no mutations (41% and 49%, respectively; P < .001). Failure-free survival among the 100 patients with chronic phase chronic myeloid leukemia when resistant mutations were detected at switchover by sequencing or mass spectrometry alone was 0% and 0% compared with 51% and 45% for patients with other mutations or no mutations (P = .003).
  
  
  CONCLUSIONS
  Detection of low-level mutations after imatinib resistance offers critical information to guide subsequent therapy selection. If an inappropriate kinase inhibitor is selected, there is a high risk of treatment failure with clonal expansion of the resistant mutant.
authors: SA Pathology, IMVS, e Rd, PO Box 14 Rundle Mall, Adelaide, SA, 5000, Australia. wendy.parker@health.sa.gov.au
authors: Wendy T
authors: WT
authors: Parker
authors: Rebecca M
authors: RM
authors: Lawrence
authors: Musei
authors: M
authors: Ho
authors: Darryl L
authors: DL
authors: Irwin
authors: Hamish S
authors: HS
authors: Scott
authors: Timothy P
authors: TP
authors: Hughes
authors: Susan
authors: S
authors: Branford
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D001549:Benzamides; D000069439:Dasatinib; D019008:Drug Resistance, Neoplasm; D016044:Fusion Proteins, bcr-abl / Q000235:genetics*; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000235:genetics*; D013058:Mass Spectrometry; D009154:Mutation; D010879:Piperazines / Q000627:therapeutic use*; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use*; D011743:Pyrimidines / Q000627:therapeutic use*; D013844:Thiazoles / Q000627:therapeutic use; D016896:Treatment Outcome
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D013844:Thiazoles; D000068877:Imatinib Mesylate; D016044:Fusion Proteins, bcr-abl; C498826:nilotinib; D000069439:Dasatinib