Midostaurin in Combination with Idarubicin and Cytarabine (3+7) Induction for FLT3 Positive AML - Very High Complete Response Rates and Transition to Allogeneic Transplantation

Abstract Background: The CALGB 10603 RATIFY trial demonstrated that midostaurin, a multi-targeted small molecule FLT3 inhibitor, when given in combination with standard 3+7 induction consisting of daunorubicin 60mg/m2 for 3 doses and cytarabine 200mg/m2/day for 7 days significantly prolonged overall survival (OS) compared to placebo plus standard induction in FLT3 positive acute myeloid leukemia (AML) patients. The safety and efficacy of the other anthracycline commonly utilized in standard AML induction, idarubicin, has not been evaluated to date. Methods: A single-center retrospective review from May 2017 to July 2018 was performed. Patients were included if they had a diagnosis of FLT3 positive AML and received induction chemotherapy with idarubicin. The primary outcome was incidence of adverse effects attributed to midostaurin. Grading of adverse effects was in accordance with the Common Terminology and Criteria of Adverse Effects (CTCAE) version 5. Additional outcomes included OS, relapse-free survival (RFS), similar as in the Ratify trial, as well as detection of FLT3 on subsequent bone marrow biopsies. Results: Ten patients were included. All patients received induction therapy with idarubicin 12mg/m2 for 3 doses and cytarabine 100mg/m2/day for 7 days. Median age was 53 years (range: 33 to 66) and 6/10 were male. Eight of 10 patients exhibited internal tandem duplication (ITD) on diagnosis; two had FLT3 tyrosine kinase domain (TKD) D835. Eight patients had diploid cytogenetics; the other two patients had core-binding factor AML. Midostaurin was initiated on day 8 of induction in all but 2 patients, who started on day 11 and 12, respectively. Nine of ten patients completed all 28 planned doses of midostaurin. All patients received antifungal prophylaxis with micafungin throughout the course of midostaurin. The median time from day 1 of induction to neutrophil (>500/µl) and platelet (>100,000/µl) recovery was 23 days and 26 days, respectively. Granulocyte colony stimulating factor (G-CSF) was initiated for all patients after day 14 bone marrow biopsy, as per institutional procedure. Four of 10 patients experienced an adverse event attributed to midostaurin. Maculopapular rash was observed in 3 patients a median of 5 days after midostaurin initiation: 2 of 3 patients had a grade 2 rash and continued therapy with topical steroids; one patient had a grade 3 rash and discontinued midostaurin after 17 of 28 planned doses. A grade 1 drug fever was attributed to midostaurin in a fourth patient. Fevers persisted despite neutrophil recovery and subsequently dissipated after completion of the final midostaurin dose. Persistent FLT3 mutation was detected in 4/9 (1 not reported) day 14 bone marrow biopsies but was negative in 9/10 pts on day 28. The lone positive FLT3 result on day 28 occurred in a patient with refractory disease (>5% blasts) necessitating salvage therapy. Notably, this patient only completed 17 of 28 planned doses. All other patients exhibited a complete response (CR) on day 28. The median follow-up time was 243 days (range: 57 to 394). Nine patients are alive at the time of reporting. Six patients proceeded to allogeneic transplantation -one death was attributed to transplant-related complications, occurring in the same patient needing salvage and reduced duration midostaurin. Two patients relapsed a median of 184 days after start of induction -both FLT3-ITD positive and neither having undergone allogeneic transplant prior to relapse. Conclusions: Midostaurin in combination with idarubicin-based induction 3+7 therapy in this first case series appears to be safe. While the incidence of rash was higher (30%) than reported in RATIFY, this only resulted in discontinuation of therapy in one patient. Although patient numbers are limited, 90% achieved a FLT3 negative CR after completion of induction therapy and six patients proceeded to allogeneic transplantation. A confounding variable includes the routine use of G-CSF, which likely contributed to the shorter duration from induction to neutrophil recovery observed compared to RATIFY (23 days vs 26 days). The influence of G-CSF use on outcome is uncertain, however represents an interesting observation. A randomized, prospective trial comparing midostaurin in combination with idarubicin versus daunorubicin at both 60mg/m2 and 90mg/m2 is warranted to establish the optimal anthracycline induction therapy for FLT3 mutated AML patients. Disclosures Al-Homsi: Celyad: Membership on an entity's Board of Directors or advisory committees. Diefenbach: Denovo: Research Funding; Merck: Consultancy, Research Funding; Acerta: Research Funding; Incyte: Research Funding; Trillium: Research Funding; Millenium/Takeda: Research Funding; Bristol-Myers Squibb: Consultancy, Research Funding; Genentech: Consultancy; Seattle Genetics: Consultancy, Research Funding.