Benefits of Early Switching From Imatinib to a Second-Generation Tyrosine Kinase Inhibitor Following 12 Month Complete Cytogenetic Response Failure: A Chart Review Analysis.
Authors: DeAngelo Daniel J. , Chen Lei , Guerin Annie , Styles Amy , Aberki Clemence , Giguere-Duval Philippe , Wu Eric Qiong 
Published: October 2019

Abstract
Abstract 2792

Background:
The National Comprehensive Cancer Network (NCCN) guidelines (version 1.2013) recommend that patients with chronic myelogenous leukemia in chronic phase (CML-CP) should be tested for cytogenetic response 12 months following imatinib initiation. Failure to achieve complete cytogenetic response (CCyR) at 12 months should result in either an increased dose of imatinib (up to 800mg) or a change to a second-generation tyrosine kinase inhibitor (TKI). This study observed patients who failed to achieve CCyR at 12 months following the initiation of imatinib and compared treatment response rates and disease progression between patients who switched to a second-generation TKI early versus patients who did not.

Methods:
An online chart abstraction form was used to survey US oncologists and hematologists. Physicians submitted de-identified information on up to 10 adult patients with CML-CP who initiated imatinib as first line therapy (between 01/01/2007 and 26/07/2010) and failed to achieve CCyR at 12 months (between 10–14 months). Patients either switched to a second-generation TKI within 3 months following CCyR failure (early-switchers), or remained on imatinib for ≥3 months following CCyR failure (non-switchers). Non-switchers may have later switched to a second-generation TKI. The index date was defined as the date of the 12-month CCyR failure. Detailed patient information was collected, including demographics, comorbidities, imatinib dosage, and hematologic and cytogenetic response prior to the index date. Cytogenetic response and disease progression was also collected after the index date. CCyR was defined as 0% Philadelphia chromosome positive (Ph+) cells on cytogenetic testing. The proportion of patients achieving CCyR by 6, 12, and 24 months was reported among patients who had ≥1 cytogenetic test during these periods. Documented CCyR was defined as CCyR achievement analyzed among all patients, if patients were not tested for CCyR following the index date they were considered not to have achieved CCyR. Time to first documented CCyR achievement and time to disease progression were both estimated using multivariate Cox proportional hazard ratios (HR), where exposure was calculated from the index date to the first documented CCyR achievement, or to the date of progression, respectively. Multivariate regression analyses controlled for age, sex, race, index year, Charlson comorbidity index, imatinib dose and hematological response prior to index date, percentage of Ph+ cells and CML disease duration at index date, number of days between CML diagnosis and imatinib initiation, and rise in transcript level and chromosome abnormalities in Ph+ cells reported prior to the index date.

Results:
The majority of the 108 surveyed physicians were from a private practice (72.2%) and a small/intermediate practice size (61.1%). Physicians provided information on 593 patients who failed to achieve CCyR at 12 months; 306 were early-switchers and 287 were non-switchers. Among the non-switchers, 78 later switched to a second-generation TKI, and 104 increased imatinib dose after the index date. Patient demographics and comorbidities were similar among early-switchers and non-switchers, however, results of the 12-month cytogenetic test revealed that early-switchers had a greater number of Ph+ positive cells (51. 5 ± 16.6) compared to non-switchers (47.2 ± 13.1, p=.002). The median follow-up time was 612.5 days (range = 91–1625) and 591 days (range = 365–1623), respectively. Among patients tested for cytogenetic response during the follow-up period (274 early-switchers and 252 non-switchers), 35% of early-switchers subsequently achieved CCyR, compared to 24 % of non-switchers (p=.006). Within 6 months after the index date, 4.7% of the early-switchers achieved CCyR vs. 0.4% of non-switchers; by 12 months, 20.1% vs. 12.3% achieved CCyR; and by 24 months, 33.6% vs. 21.8% achieved CCyR, respectively (all p<.016). After adjusting for confounding factors, early-switchers had an 80% greater documented CCyR achievement rate compared to that of non-switchers (HR=1.80; p=.002) and a progression rate that was 81% lower (3.8% vs.1.5%, HR=0.19, p=.034).

Conclusion:
Early switching from imatinib to a second-generation TKI following 12-month CCyR failure was associated with better cytogenetic response and a lower risk of progression.

Disclosures:
DeAngelo: Novartis: Consultancy. Off Label Use: Everolimus in AML. Chen:Novartis Oncology: Employment, Own stock in Novartis Other. Guerin:Analysis Group, Inc.: Consultancy, Employment, I am an employee of Analysis Group, Inc, which has received consulting fees from Novartis Pharmaceuticals Other, Research Funding. Styles:Analysis Group, Inc.: Consultancy, Employment, Research Funding. Aberki:Analysis Group, Inc.: Consultancy, Employment, Research Funding. Giguere-Duval:Analysis Group, Inc.: Consultancy, Employment, Research Funding. Wu:Analysis Group, Inc.: Consultancy, Employment, I am an employee of Analysis Group, Inc, which has received consulting fees from Novartis Pharmaceuticals Other, Research Funding.