Fms-like Tyrosine Kinase 3 Ligand Concentration Kinetic Profile during Induction Is Strongly Predictive of Survivals in AML: Results of the FLAM/Flal Study

International audience ; The cytokine Fms-like tyrosine kinase 3 ligand (FL) is a key regulator of hematopoiesis. In a previous Phase 1 study testing a radioimmunotherapy regimen for relapsed/refractory acute lymphoblastic leukemia (ALL), responders showed increased soluble FL serum concentration (sFLc) after salvage regimen (Chevallier, Lancet Haematol., 2015).This prospective monocentric study (ClinicalTrials.gov NCT02693899) aimed to assess the impact of sFLc in ALL and acute myeloid leukemia (AML) patients treated according to standard-of-care intensive first-line chemotherapy regimens. Serum samples were collected on days 1, 8, 15, 22 of induction, at days 1, 8, 15 of each intensive consolidation or day 1 of each non intensive consolidation when appropriate, frozen-stored then tested by ELISA (DY308, R&D Systems, Minneapolis, MN). The following outcomes were considered to assess the impact of sFLc: refractory status after induction (≥5% bone marrow blasts or persistent aplasia >45 days), morphologic, immunophenotypic, cytogenetic or molecular relapses, event-free (EFS) and overall survival (OS). All patients provided informed consent.Between May 2016 and January 2018, 80 patients were included. Data were ultimately available for 16 ALL and 62 AML patients. A total of 579 samples were assayed. Analysis of the results disclosed 3 sFLc kinetic profiles during induction i) sustained increase from days 1 to 22 (FLI group), ii) increase from days 1 to 15, then decrease at day 22 (FLD group) and iii) stagnation of low levels all along (<1000 pg/mL from days 1 to 22, FLL group).The 16 evaluable ALL patients were classified as FLI (n=2), FLD (n=7) and FLL (n=7). All reached a cytologic complete remission after induction and only 2 relapses have been documented so far in this group. No impact of sFLc kinetic profile was seen in this context.Conversely, a significant impact of sFLc during induction (but not during consolidation) was observed in AML patients. The median age in this group was 59 years old ...