Safety and Efficacy of Combining Midostaurin and Gemtuzumab Ozogamicin with Induction Chemotherapy in FLT3 mutated AML Open Access

• Midostaurin can be safely combined with Gemtuzumab Ozogamicin (GO) and intensive induction chemotherapy in FLT3mut AML.

• The addition of midostaurin to DA+GO increased the clearance of molecular MRD assessed by RTqPCR (for NPM1 mutation) and NGS (for FLT3 ITD).

Despite the use of FLT3 inhibitors, outcomes for patients with FLT3 mutated (FLT3mut) AML remain suboptimal because of high rates of relapse. We evaluated the safety and efficacy of the combination of daunorubicin, cytarabine (DA), gemtuzumab ozogamicin (GO) and midostaurin (DAGO+m) for younger patients with newly diagnosed FLT3mut AML in the UK NCRI AML19 trial. 195 patients were randomised to receive DA with either one or two doses of GO (DAGO1 and DAGO2). 77 had a FLT3 mutation (60 had FLT3-ITD) and received midostaurin for two weeks after each chemotherapy course and then as maintainance for one year unless transplanted. 39 patients received midostaurin with DAGO1 (DAGO1+m) and 38 with DAGO2 (DAGO2+m). Their median age was 51y (range 20-74) and 16 (20%) were aged >60y. The overall response rate (CR + CRi) was 91%. Day 30 and day 60 mortality was 0% with no increase in toxicity compared to patients treated contemporaneously with DAGO1 and DAGO2 without midostaurin. 2y overall survival was 77%. 2y event-free survival and cumulative incidence of relapse were 62% and 31% respectively. MRD clearance was enhanced compared to patients with FLT3-mutated AML treated with DAGO1 and DAGO2 without midostaurin. 81% of evaluable patients were NPM1 MRD negative by RT-qPCR in the peripheral blood after course 2 (76% with DAGO1+m and 86% with DAGO2+m), 79% were MRD negative in the bone marrow by FLT3-ITD NGS, and all patients had FLT3-MRD levels below 0.01%. DAGO+m appears safe and effective . DAGO2+m will now be evaluated in a randomised study (OPTIMISE-FLT3, ISRCTN 34016918). Trial: ISRCTN78449203