Non-Canonical FLT3 Mutations (FLT3m) in Patients (Pts) with Newly Diagnosed Acute Myeloid Leukemia (AML) - Outcomes and Prognosis after FLT3 Inhibitor (FLT3i) and Venetoclax Based Regimens

Background:

Clinical trials of FLT3 inhibitors (FLT3i) have been restricted to AML pts with FLT3 Internal Tandem Duplications (ITD) and D835 tyrosine kinase domain (TKD) mutations. The impact of less common FLT3m is poorly understood. These non-canonical FLT3m occur at sites within the activation loop of the TKD2, the ATP binding pocket of the TKD1, the juxtamembrane domain (JMD), transmembrane domain (TMD) and extracellular domain (ECD). Our goal was to analyze the clinical outcomes in pts with isolated non-canonical FLT3m (non-ITD FLT3m).

Methods:

A multiplex fluorescent-based PCR analysis followed by capillary electrophoresis for detection of ITD and/or TKD mutations in FLT3 was performed on DNA isolated from BM aspirate samples. Next generation sequencing (NGS) at baseline was performed using the Illumina MiSeq platform with multigene panels (either 28-gene, 53-gene, or 81-gene) interrogating genes recurrently mutated in myeloid neoplasms. A minimum of 250× coverage with a lower limit of detection of ∼2% was used for variant calling.

Results

Among 2361 pts with newly diagnosed AML between 2012-2022 (CBF AML and APL excluded), 554 (23%) had FLT3m at diagnosis, of which 116 (5%) were non-ITD FLT3m. Among pts with non-ITD FLT3m, 54 (47%) and 62 (53%) were treated with intensive chemotherapy (IC) and low-intensity chemotherapy (LIC), respectively. IC pts received IC alone (N=29), IC + Ven (N=13), and IC + FLT3i (N=12). LIC pts received LIC alone (N= 30), LIC + Venetoclax (Ven, N=22) and LIC + Ven + FLT3 inhibitor (FLT3i, N=10). Pts who received LIC were older (69 vs 55) and more likely to have secondary and therapy-related AML (42% vs. 7%).

Among 116 pts, 75 (65%) had D835 mutations (10 pts had other co-occurring non-ITD FLT3m, 65 had isolated D835m). 22 pts had N676 mutations: 9 pts had other co-occurring non-ITD FLT3m and 13 had isolated N676m.

83 (72%) pts had TKD2 mutations, 25 (22%) pts had TKD1 mutations, and 19 (16%) pts had mutations impacting other domains. NPM1, RAS, DNMT3A, and PTPN11 were the most commonly co-mutated genes.For the entire non-ITD FLT3m cohort, the CR/CRi rate was 70%. CR/CRi rates in the IC cohort and LIC cohort were 83% and 58% respectively.

In the IC cohort rates of CR/CRi for IC + FLT3i, IC + Ven , and IC only were 67% (N=8), 92% (N=12), and 86% (N=25) respectively. Pts who received either LIC + FLT3i + Ven or LIC + Ven had higher CR/CRi rates at 90% (N=9) and 72% (N=16) when compared with LIC therapy alone with a CR/CRi rate of 37% (N=11).

In pts with D835, N676, and all other mutations the CR/CRi rates were 68% (N=51), 77% (N=17), and 71% (N=22) respectively. Rates of CR/CRi based on domains were 80%(N=20), 70% (N=58) and 63% (N=12) for TKD1, TKD2, and other domains.

Overall, 22 pts relapsed and 15 (68%), 2 (9%), and 5 (23%) pts had D835, N676, and other mutations at baseline respectively. 17 pts had FLT3 testing and NGS performed at time of relapse.12 (71%) pts were found to have FLT3m disease: 9 (53%) D835, 1 (8%) V491, 1 (8%) A680, and 1 (8%) pt who developed a new ITD mutation.

In the IC cohort, 8 pts relapsed (all among IC alone); 6 of 7 (85%) had FLT3m at relapse.

In the LIC cohort, 14 pts relapsed: 7 with LIC + Ven, 3 with LIC + Ven + FLT3i, and 4 with LIC alone. Nine had FLT3 testing with 6 pts relapsing with FLT3m disease, all in the cohorts without FLT3i.

Median follow-up was 36 mo. The median OS in pts with ITD and non-ITD FLT3 mutations were 17.7 and 14.9 mo (p= 0.65, Figure 1A). In pts with D835, N676, and other non-ITD FLT3m the median OS was 13.7 mo, 13.9 mo, and NR respectively (Figure 1B). OS based on domain were 12.2 mo, 15.2 mo, and not reached (NR) for TKD1, TKD2, and mutations involving other domains.

Within the IC cohort, the median OS for IC alone, IC + FLT3i and IC + Ven was 30.9 mo, NR and NR respectively. Median RFS for the IC + FLT3i and the IC + Ven has not been reached. The median RFS for IC alone is 56 mo.

In LIC cohort, OS rates were 4.2, 29.9, and 16.2 for LIC alone, LIC + FLT3i + Ven, and LIC + Ven. RFS was similar for all three LI regimens: 15.8, NR, and 14.8mo.

Conclusion

The OS of pts with ITD and non-ITD FLT3m was similar. Pts with D835, N676 and other non-ITD FLT3m had similar response to induction chemotherapy with comparable OS rates. The majority of the relapses (71%) were positive for FLT3m. Relapse associated with FLT3 D835 (53%) was most common. No FLT3 N676 positive relapses were observed. Relapse occurred exclusively in pts who received LIC regimens or IC only. No relapses were observed in pts who received IC in combination with FLT3i or Ven.

Daver:Agios, Celgene, SOBI and STAR Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees; Kartos and Jazz Pharmaceuticals: Other: Data monitoring committee member; Karyopham Therapeutics and Newave Pharmaceutical: Research Funding; Astellas, AbbVie, Genentech, Daiichi-Sankyo, Novartis, Jazz, Amgen, Servier, Karyopharm, Trovagene, Trillium, Syndax, Gilead, Pfizer, Bristol Myers Squibb, Kite, Actinium, Arog, Immunogen, Arcellx, and Shattuck: Consultancy, Other: Advisory Role; Astellas, AbbVie, Genentech, Daiichi-Sankyo, Gilead, Immunogen, Pfizer, Bristol Myers Squibb, Trovagene, Servier, Novimmune, Incyte, Hanmi, Fate, Amgen, Kite, Novartis, Astex, KAHR, Shattuck, Sobi, Glycomimetics, Trillium: Research Funding. Loghavi:Astellas: Research Funding; Amgen: Research Funding; Abbvie: Consultancy, Current equity holder in publicly-traded company; QualWorld: Consultancy; GLG: Consultancy; PeerView: Honoraria. Kadia:Novartis: Consultancy; Servier: Consultancy; Pfizer: Research Funding; cyclacel: Research Funding; AstraZeneca: Research Funding; Ascentage: Research Funding; Delta-Fly: Research Funding; Amgen: Research Funding; Genfleet: Research Funding; Astex: Honoraria; Regeneron: Research Funding; Genentech: Consultancy, Research Funding; Glycomimetics: Research Funding; PinotBio: Consultancy; Astellas: Research Funding; JAZZ: Consultancy, Research Funding; Iterion: Research Funding; Agios: Consultancy; cellenkos: Research Funding; BMS: Consultancy, Research Funding; Abbvie: Consultancy, Research Funding. Short:Amgen: Consultancy, Honoraria; Stemline Therapeutics: Research Funding; AstraZeneca: Consultancy; Astellas: Research Funding; Takeda Oncology: Consultancy, Research Funding; Novartis: Consultancy; Pfizer: Consultancy. DiNardo:Servier: Consultancy, Honoraria, Research Funding; Astex: Research Funding; AbbVie: Consultancy, Research Funding; Kura: Honoraria, Membership on an entity's Board of Directors or advisory committees; GenMab: Membership on an entity's Board of Directors or advisory committees; GlaxoSmithKline: Membership on an entity's Board of Directors or advisory committees; Bluebird Bio: Honoraria; Jazz: Honoraria; Takeda: Honoraria; Novartis: Honoraria; Cleave: Research Funding; Forma: Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Astellas: Honoraria; Notable Labs: Current holder of stock options in a privately-held company, Membership on an entity's Board of Directors or advisory committees; LOXO: Research Funding; ImmuneOnc: Honoraria, Research Funding; Foghorn: Honoraria, Research Funding; Gilead: Honoraria. Borthakur:Astex Pharmaceuticals, Ryvu, PTC Therapeutics: Research Funding; Pacylex, Novartis, Cytomx, Bio Ascend: Membership on an entity's Board of Directors or advisory committees; Catamaran Bio, Abbvie, PPD Development, Protagonist Therapeutics, Janssen: Consultancy. Garcia-Manero:Novartis: Honoraria, Research Funding; Genentech: Honoraria, Research Funding; Astex: Consultancy, Honoraria, Research Funding; Curis: Honoraria, Research Funding; Acceleron Pharma: Consultancy; Aprea: Honoraria; Gilead Sciences: Research Funding; BMS: Consultancy, Honoraria, Research Funding; AbbVie: Honoraria, Research Funding. Ravandi:AstraZeneca: Consultancy; Abbvie: Consultancy, Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Novartis: Consultancy; Biomea Fusion, Inc.: Research Funding; Astex/Taiho: Membership on an entity's Board of Directors or advisory committees, Research Funding; Amgen: Honoraria, Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Syos: Consultancy, Honoraria, Research Funding; BMS/Celgene: Consultancy, Honoraria, Research Funding; Prelude: Research Funding; Xencor: Research Funding. Kantarjian:Novartis: Honoraria, Research Funding; Jazz Pharmaceuticals: Research Funding; Astellas Health: Honoraria, Membership on an entity's Board of Directors or advisory committees; Ascentage: Membership on an entity's Board of Directors or advisory committees, Research Funding; KAHR Medical Ltd: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria, Research Funding; Ipsen Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees; ImmunoGen: Research Funding; Amgen: Honoraria, Research Funding; Daiichi-Sankyo: Consultancy, Research Funding; NOVA Research: Honoraria; Pfizer: Honoraria, Research Funding; Takeda: Honoraria. Yilmaz:Daiichi-Sankyo: Research Funding; Pfizer: Research Funding.