Frontline Treatment With Imatinib Mesylate in Chronic Myeloid Leukemia Patients in Early Chronic Phase: a Very Long-Term Analysis by the GIMEMA CML Working Party
Authors: Castagnetti Fausto , Gugliotta Gabriele , Breccia Massimo , Specchia Giorgina , Intermesoli Tamara , Capucci Adele , Martino Bruno , Tiribelli Mario , Binotto Gianni , Abruzzese Elisabetta , Stagno Fabio , Leoni Pietro , Ferrero Dario , Gherlinzoni Filippo , Palandri Francesca , Venturi Claudia , Bochicchio Maria Teresa , Soverini Simona , Alimena Giuliana , Martinelli Giovanni , Pane Fabrizio , Saglio Giuseppe , Cavo Michele , Baccarani Michele , Rosti Gianantonio 
Published: October 2019

Abstract

Background
The chronic myeloid leukemia (CML) therapeutic scenario has been enriched by the approval of second generation TKIs as frontline treatment of early chronic phase (ECP) patients, but imatinib mesylate (IM) still represents the standard for many patients. The long term outcome is extremely important to assess the treatment efficacy and to decide on the allocation of resources. The phase 3 trials comparing second generation TKIs versus standard-dose IM have not still demonstrated a clear improvement in terms of progression-free survival and overall survival. In the IRIS trial, at 8 year, 55% of patients were still on IM and the overall survival (OS) was 85%. Other published reports have shorter follow-up.

Aims and Methods
To assess the very long-term outcome of CML patients treated frontline with IM, we analyzed 559 patients enrolled within 3 multicentric prospective studies conducted by the GIMEMA CML Working Party (NCT00514488, NCT00510926, observational trial CML023). Definitions: major molecular response (MMR), BCR-ABLIS ratio <0.1%; deep molecular response (MR4.0), detectable disease ≤ 0.01% BCR-ABLIS or undetectable disease with ≥10,000 ABL transcripts; progression, transformation to accelerated or blastic phase; failure, according to 2013 ELN criteria; event, treatment discontinuation for any reason or lost to follow-up. Information on survival and progression were regularly collected. All deaths, at any time and for any reason, were included. All the analysis have been made according to the intention-to-treat principle.

Results
Baseline demographics characteristics: median age: 52 years (extremes 18-84 years); male sex: 60%; high Sokal, high Euro and high EUTOS scores: 22%, 7% and 7%, respectively; clonal chromosomal abnormalities (CCA) in Ph+ cells: 4% (not evaluable in 32% of patients for insufficient number of metaphases); e13a2 BCR-ABL transcript: 36%. Median follow-up: 76 (7-99) months. The cumulative incidence of complete cytogenetic response (CCyR), MMR and MR4 was 88%, 85% and 61%, respectively. The median time to CCyR, MMR and MR4 was 6, 7 and 42 months, respectively. Patients with high Sokal, high Euro and high EUTOS scores had significantly lower overall estimated probability of CCyR and MMR with respect to low and intermediate risk patients. A high Sokal score also predicted a significantly inferior probability of MR4; patients with high Euro and high EUTOS score had lower overall estimated probability of MR4, but the difference were not statistically significant. The reasons for IM discontinuation were: lack of efficacy (19%), toxicity or death (9%), withdrawal of informed consent (3%); 4% of patients were lost to follow-up. The 8-year event-free survival (EFS), failure-free survival (FFS), progression-free survival (PFS) and OS were 55% (95% CI: 51-60%), 66% (95% CI: 61-70%), 84% (95% CI: 78-89%) and 85% (95% CI: 79-90%), respectively. A high Sokal and a high Euro scores were able to identify patients with significantly lower probability of EFS, FFS, PFS and OS with respect to the other patients. High EUTOS score patients had significantly poorer EFS and FFS, but PFS and OS differences were not significant. Age, performance status and e13a2 transcript resulted independent prognostic factors on PFS and OS.

Conclusions
Until now, the available data on the very long-term outcome of newly diagnosed chronic phase CML patients treated frontline with imatinib are limited to a company sponsored study (IRIS study). The GIMEMA CML Working Party provided an unbiased overview of the long-term imatinib therapeutic effects in a multicentric nationwide experience. These results should be taken into consideration to make treatment decision concerning the choice of the first line TKI, particularly in low risk patients.

Acknowledgments
University of Bologna, BolognaAIL, COFIN, Fondazione Carisbo.

Disclosures:
Castagnetti: Novartis Farma: Consultancy, Honoraria; Bristol Myers Squibb: Consultancy, Honoraria. Gugliotta:Novartis: Consultancy, Honoraria; Bristol-Myers Squibb: Consultancy, Honoraria. Abruzzese:BMS, Novartis: Consultancy. Soverini:Novartis: Consultancy; Bristol-Myers Squibb: Consultancy; ARIAD: Consultancy. Cavo:Celgene: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Janssen: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Millennium: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Onyx: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees; Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity’s Board of Directors or advisory committees.