TKI Treatment Discontinuation: How Many Patients Could Stop Tyrosine Kinase Treatment According to Discontinuation Trials Criteria? Incidence and Prognostic Impact of Deep Molecular Response in a Cohort of Chronic Myeloid Leukemia Patients of South Brazil's Hematology Centers
Authors: Fogliatto Laura , Capra Marcelo Eduardo Zanella , Shaan Mariza , Vanelli Costa Tito , Contin Luis Carlos Zanandrea , Breunig Raquel , Silveira Juarez Fontoura , Torriani Mayde Seadi , Fassina Katia , Fernandes Mario Sergio , Almeida Denise , Schilling Marco Antonio , Hellwig Tânia , Daltoe Tiago , Moschen Mariangela , Zardo Adriana , Nene Moema , Daudt Liane Esteves , Friedrisch João , Silla Lucia 
Published: October 2019

Abstract
Sustained deep molecular response (MR4.5) after imatinib treatment defines a subgroup of patients with chronic myeloid leukemia (CML) with better outcome and that probably would be able to stop treatment in the future, according to results of clinical TKI discontinuation trials. Most of these trials showed that patients with a long-term imatinib treatment and low Sokal risk have a higher probability of maintain a deep molecular remission after stopping treatment.
OBJECTIVES
The main objective is to review the molecular responses, overall survival and event free survival of CP CML patients that have been treated with imatinib in 14 hematology centers in South Brazil. Using our data basis we also would like to see how many of them present long-term imatinib treatment, sustained deep molecular remission and correlate these findings with the Sokal risk groups. These data would allow us to predict patient profile that could be able to discontinue the treatment in the future in a prospective clinical trial.
PATIENTS AND METHODS
This is a retrospective study in a cohort of pts with chronic myeloid leukemia chronic phase (CP) that have been treated in 14 hematology centers in South Brazil. All pts received imatinib 400mg as first or second-line therapy. Patient evaluation and response criteria followed the ELN recommendations. MR(4.5) was defined as ≥ 4.5 log reduction of BCR-ABL on the international scale (IS) and determined by reverse transcriptase polymerase chain reaction. All tests were performed at a central standardized according to ELN. Event-free-survival (EFS) was measured from the start of imatinib to the date of any of the following events while on therapy: death from any cause, loss of complete hematologic response, loss of complete cytogenetic response, discontinuation of therapy for toxicity or lack of efficacy, or progression to accelerated phase or blastic phase. Overall survival (OS) was measured from the start of imatinib until death of any cause or to the date patient was last known to be alive.
RESULTS
Data from 474 patients was analyzed. After a median observation time of 46 months, 5-year overall survival (OS) was 86%, 5-year event-free-survival was 53%. Of the 474 patients, 258 had adequate PCR evaluations during treatment. 118 of 258 (45,7%) patients achieved MR(4.5) and 69 of 258 (27%) had sustained response for at least two years after a minimum time of treatment of 3 years. The cumulative incidence of MR(4.5) after 9 years was 76% (median, 3 years). In the group that achieved MR(4.5), there was only 1 (0,8%) death and 1 (1,1%) progression compared to 8 deaths (5,7%) and 8 progressions (7,5%) in the group without MR(4.5); these differences were significant with p=0,03 and 0,02 respectively. In the subgroup of 69 patients that had had been treated with imatinib for 3 year or more and sustained deep response (RM4,5) for at least two years, 21 pts had low Sokal risk, 7 pts intermediate Sokal risk and only 4 pts a high Sokal risk. Unfortunately, in 37 pts the Sokal risk could not be accessed due to missing information.
CONCLUSION
In our series MR(4.5) is reached in the majority of patients with long-term imatinib treatment. MR(4.5) is a predictor of outcome with only one disease progression and one death due to CML in this group of patients. Unfortunatly PCR are not available for all patients in our clinical practice, but this situation are improving. Regarding the 69 patients with TKI discontinuation trial criteria, we find out that 21 patients fulfill such criteria. In the future, according to the results of current stop trials it could be possible include this selected group of CP CML patients in a prospective clinical trial.

Disclosures
No relevant conflicts of interest to declare.