FINAL Analysis of a PAN European STOP Tyrosine Kinase Inhibitor Trial in Chronic Myeloid Leukemia : The EURO-SKI Study
Authors: Mahon Francois-Xavier , Richter Johan , Hochhaus Andreas , Panayiotidis Panayiotis , Medina de Almeida Antonio , Mayer Jiri , Hjorth-Hansen Henrik , Janssen Jeroen , Mustjoki Satu , Martínez-López Joaquín , Vestergaard Hanne , Ehrencrona Hans , Kairisto Veli , Dulucq Stephanie , Machova Katerina , Nicolini Franck E. , Hofmann Wolf-Karsten , Guilhot Joelle , Saussele Susanne , Pfirrmann Markus 
Published: November 2021

Abstract

Background: With the dramatic success of tyrosine kinase inhibitors (TKI) to treat Chronic myeloid leukemia (CML), the life expectancy of CML patients is now close to that of the general population. In addition, treatment cessation is now a realistic goal for some CML patients. This was shown by several clinical trials such as the STIM study leading to the concept of TFR (treatment free remission). Around 40-60% of patients with stable DMR [deep molecular response, corresponding to &lt;0.01% BCR-ABL (IS)] can stop the TKI successfully, e.g. in accordance with recommendations from the European LeukemiaNet. In the interim analysis of the first 200 patients of the EURO-SKI (European Stop TKI) trial, 62% were in major molecular response (MMR: &lt;0.1% BCR-ABL1 IS) at 6 months. DMR duration before TKI stop was most predictive for maintenance of MMR. Here we present the final analysis of the EURO-SKI trial after 3 years of follow-up.
Aims: The main objectives of The EURO-SKI trial were the evaluation of molecular recurrence-free survival (MRecFS) after Stopping TKI in a large Pan-european cohort of CML patients and definition of prognostic markers to increase the rate of patients in durable deep MR after stopping TKI. Further aims are the evaluation of harmonized methods of molecular monitoring.
Methods: Adult CML patients in chronic phase CML on TKI treatment in confirmed DMR for at least one year (confirmed by three consecutive PCR tests) and under TKI treatment for at least 3 years were eligible. DMR confirmation was performed in standardized laboratories. Primary endpoint was maintenance of MMR after stopping TKI. According to protocol, a 36 months follow-up was planned. The null hypotheses were that MMR maintenance at 6 and 36 months was less or equal than 40% and less or equal than 35%, respectively.
Results: Between May 2012 and December 2014, 868 patients were pre-registered by 61 centers from 11 countries. 140 pts were excluded (consent withdrawal n=1, protocol violation n=38, not eligible n=74, DMR not confirmed n=11, atypical/unknown transcript n=15, missing data n=1) resulting in 728 eligible patents. Of these, 46.8% were female. Median age at diagnosis was 52 years (range, 11 to 85 years). Median duration of TKI treatment was 7.5 years (range, 3.0-14.1 years) and median duration of MR4 before TKI cessation was 4.7 years (range, 1.0-13.3 years). Nine patients died without MMR loss (none CML related), 15 patients restarted TKI without MMR loss. At 6 months, 713 patients were available (without molecular test at 6 months: n=6, TKI restart without relapse: n=9). Since 434 patients (61%) [95% CI: 57-64] remained without relapse during the first 6 months, the null hypothesis was rejected (p&lt;0.0001). At 36 months, 678 patients could be analyzed (TKI restart without relapse: n=17, no molecular test at 36 months: n=33). With 309 patients in MMR, corresponding to 46% [95% CI: 42-49], the null hypothesis of 35% or less was rejected (p&lt;0.0001). MRecFS at 36 months resulted in 48% (CI: 44-52%) and molecular recurrence- and treatment-free survival (MRecTFS) in 46% (CI: 43-50%) (Fig 1). No blast crisis occurred.
Regarding prognostic factors, we confirmed that TKI treatment duration and DMR duration were still the most important factors to predict MMR loss at 6 months. For the late recurrence, i.e., between 6 and 36 months (57 patients), TKI treatment duration before stop was the only relevant variable in a preliminary univariate logistic analysis.
Summary/Conclusion: With this final analysis of the largest TFR trial, we confirm the MRecFS and MRecTFS rates at 6 months previously obtained from the interim analysis. However, late molecular recurrence (15% between 6 and 36 months) occurred and the underlying mechanisms need to be discussed. Nevertheless, 46% of the patients, were still in MRecTFS at 3 years.
Figure 1 Figure 1.

Disclosures
Hochhaus: Bristol-Myers Squibb: Research Funding; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Research Funding; Incyte: Research Funding. Hjorth-Hansen: AOP: Research Funding; Novartis: Research Funding; Pfizer: Research Funding. Mustjoki: Novartis: Research Funding; BMS: Research Funding; Janpix: Research Funding; Pfizer: Research Funding. Martínez-López: Roche, Novartis, Incyte, Astellas, BMS: Research Funding; Janssen, BMS, Novartis, Incyte, Roche, GSK, Pfizer: Consultancy. Nicolini: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel, accommodations, expenses, Research Funding; Incyte Biosciences: Honoraria, Other: travel, accommodations, expenses, Research Funding, Speakers Bureau; Kartos Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Sun Pharma Ltd.: Consultancy, Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria. Saussele: Roche: Honoraria; Pfizer: Honoraria; Incyte: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding.