Early Assessment of Molecular Response in Chronic Myeloid Leukemia Patients On Dasatinib After Imatinib Failure Identify Patients with Poor Cytogenetic and Molecular Responses
Authors: Pagnano Katia B. , Ribeiro Beatriz F , Miranda Eliana C M , Delamain Marcia T , De Souza Carmino Antonio , Duarte Gislaine O , Vergilio Bruna , Albuquerque Dulcinéia Martins , dos Santos Andrey , Tavares Anderson , Lorand-Metze Irene 
Published: October 2019

Abstract
Abstract 3787
Dasatinib is effective at inducing complete cytogenetic response (CCyR) in approximately half of chronic myeloid leukemia (CML) patients treated in the chronic phase (CP) after failing imatinib. The aim of this work was to evaluate the role of molecular monitoring in predicting the outcome of patients treated with dasatinib after imatinib therapy.
Between 2008 and 2012, it was analyzed 55 consecutive patients with CML with imatinib intolerance or resistance treated in a single center. Patients received dasatinib (50–140 mg) as second or third line therapy. Cytogenetic analysis was performed at 3, 6, 12 and 18 months after dasatinib introduction. BCR-ABL1 transcripts were measured in the blood at 3 months intervals using real-time quantitative PCR (RQ-PCR). Results were expressed as percent ratios relative to an ABL1 internal control. Major molecular response (MMR) was defined as a transcript level ≤ 0.1% on the international scale. Kinase domain (KD) mutations were performed before starting therapy and/or after dasatinib resistance. The probabilities of overall survival (OS), progression-free survival (PFS), and event-free survival (EFS) were calculated using the Kaplan-Meier method. An event was defined as the loss of a CCyR or complete hematologic response, progression to AP and BP, death, or discontinuation of dasatinib. The probabilities of cytogenetic and molecular responses were calculated using cumulative incidence (CI) and x2method.

Results:
33 patients were male (60%) and 22 female (40%), with median age of 48 years (15–81). At diagnosis Sokal scores were low for 11/34 (32.4%), intermediate for 6 (17.6%) and high for 17 (50%) (21 NA). Thirteen patients had a previous CCyR with imatinib. The median time between diagnosis and dasatinib treatment was 25 (2–223) months. The median follow-up was 12 months. Disease phase at beginning of dasatinib treatment: 32 (58%) CP, 13 (24%) accelerated phase (AP) e 10 (18%) blast phase (BP). Eight-seven percent achieved RHC, 55% CCyR and 38% MMR. At 3 months 67% (25/37) had BCR-ABL1/ABL1 transcript ratio '10%, at 6 months 48% (14/29) ≤ 1% and at 12 months 27% (6/22) RQ-PCR ≤ 0.1%. After introduction of dasatinib, patients with the 3-month BCR-ABL1/ABL1 transcript ratio of >10% had a lower chance of achieving CCyR (12.5% vs 81.5%, p= 0.001) and MMR (8.3% vs. 58.3%, p= 0.005). Patients with the 6-month BCR-ABL1/ABL1 transcript ratio of >1% had a lower chance of achieving CCyR (8% vs. 75%, p= 0.01) and MMR (26.6% vs. 64.2%, p=0.06) compared with patients with ratio ≤ 1%. The probability of OS, PFS and EFS in 48 months while on treatment was 83%, 70% and 29%, respectively. PFS was 88%, 76% e 11% in CP, AP and BP respectively (p< 0.0001). EFS was 36%, 32% e 10% in CP, AP and BP (P< 0.0001). Dasatinib was discontinued in 26/55 because of resistance (12), intolerance (5) or transplant (1). BCR-ABL KD mutations were detected in 13/38 cases, two before (L387M e M351T) and 11 during dasatinib treatment (T315I-6, M244V-2, E255V-1, E499E-1, M351T-1). Patients with mutations had an inferior EFS (p=0,05).
In conclusion, this study indicates that evaluation of molecular response at 3 and 6 months can identify patients with less chance of response to dasatinib in patients with imatinib failure. The early identification of patients with poor outcome is important for planning future treatments.

Disclosures:
No relevant conflicts of interest to declare.