Impact of ABL kinase domain mutations on the outcome of patients with chronic myeloid leukemia (CML).

Abstract

6588 Background: Patients with CML who develop resistance to imatinib commonly have mutations in the BCR-ABL kinase domain (KDM). Studies looking at outcomes in patients with P-loop versus non-P-loop mutations within the ABL-Kinase Domain have produced conflicting results. Methods: The Total Cancer Care (TCC) database was used to identify patients with CML treated at Moffitt Cancer Center (MCC). Descriptive data were reported, chi square test was used for categorical variables, and Kaplan Meier curves were used for OS and PFS. Log rank test was used to compare survival times between groups. Results: Between 1992 and 2011, 540 CML patients were treated at MCC. Of those, 51% were male and 71% were under the age of 60. Sixty percent (n=322) were diagnosed after 2001. Of the 540 patients, 6.5% (n=35) were found to have mutations of which 26 were detected in patients diagnosed after 2001. Of the 35 patients, 74% (n=26) had single mutations and 26% (n=9) had compound mutations. P-loop mutations were seen in 17% (n=6) and 43% (n=15) had T315I mutations. Patients with KDM progressed to accelerated or blast phase in 46% (n=16) of cases compared to 27% (n=136) without mutations (p=0.03). Median OS was 126 months, 109 months, and not reached in patients with P-loop, T315I, and non-P-loop mutations respectively (p=0.17). The corresponding median PFS was 85 months, 89 months, and not reached (p=0.20). In patients with one mutation median OS was not reached compared to 105 months in patients with compound mutations (p=0.27). After 2001, patients with KDM had a median PFS of 75 months and OS of 126 months while neither was reached in the non-mutation cohort (p=0.007, p=0.26 respectively). Median PFS in patients with single mutations was 85 months versus 10 months in those with compound mutations (p=0.037). Patients with KDM had additional Ph+ clones on cytogenetics in 49% of cases compared with 19% of cases in the non-mutation group (P < 0.005). Conclusions: T315I and P-loop KDM predict PFS and OS in CML patients, and convey a trend for worse prognosis. The presence of additional Ph+ clones in patients with BCR-ABL KDM indicates a higher level of genetic instability and clonal evolution, which may be the contributing factor to poor outcomes.