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Treatment Option Overview

    Table 6. Relationship Between Tyrosine Kinase Genotype and Response to Imatinib Therapya

    European Phase I/IIb Trial, % (n)[31]B-2222 Phase IIc Trial, % (n)[32]European/Australasian Phase IIId Trial, % (n)[18]North AmericanCLB-80004Phase IIIe Trial, % (n)[33]
    N = number in sample, number of observations; NR = not reported.
    a Annual review of pathology by ANNUAL REVIEWS, INC. Reproduced with permission of ANNUAL REVIEWS, INC., in the format Internet posting via Copyright Clearance Center.[3]
    b[Level of evidence: 1iiA, 1iiDii,1iiDiv (Phase 1) and2A; 2Div(Phase II)]
    c[Level of evidence: 1iiDiv]
    d[Level of evidence: 1iiAand1iiDiii]
    e[Level of evidence: 1iiDiv]
    f Defined as complete or partial response by Southwest Oncology Group (SWOG) criteria for B-2222 or RECIST (Response EvaluationCriteria in Solid Tumors) for all other trials; excludes nonevaluable patients.
    g Statistically significant difference compared toKIT9 and wild-type (noKITorPDGFRAmutation) groups.
    Study participants(N = 37)(N = 127)(N= 377)(N = 324)
    Objective responsef 
    KITexon 1183 (24)83g(85)70g(248)67g(211)
    KIT exon 925 (4)48 (23)35 (58)40 (25)
    Wild-type33 (6)0 (9)25 (52)39 (33)
    Progressive disease 
    KIT exon 11453NR
    KIT exon 901717NR

    Kinase genotype appears to correlate with progression-free survival (PFS) and OS. The median time to tumor progression (TTP) for patients whose GIST harbors a KIT exon 11 mutation has been reported to be more than 1 year longer than the median TTP for patients whose tumors have KIT exon 9 or wild-type kinase genotypes; a similar OS benefit has been reported for patients with KIT exon 11 mutations versus the other common genotype subsets.[3] In a subset analysis of the European/Australasian phase III trial, it was found that the PFS of GIST patients with KIT exon 9 mutations was significantly better when patients were treated with 800 mg of imatinib per day as compared with 400 mg per day (P = .0013), with a reduction of relative risk of 61%.[18][Level of evidence: 1iiDiii] Accordingly, routine tumor typing and imatinib dose selection based on the presence or absence of a KIT exon 9 mutation is recommended by some but not all GIST experts.[3,4]


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