Pooled Safety Analysis of Quizartinib Monotherapy in Patients with Relapsed/Refractory (R/R) Acute Myeloid Leukemia (AML)

Background: Quizartinib is a once-daily, oral, highly potent and selective FLT3 inhibitor with proven single-agent activity and a manageable safety profile in FLT3-ITD R/R AML. In the global, phase 3 QuANTUM-R study, quizartinib demonstrated a significant survival benefit over salvage chemotherapy(Cortes, et al. Lancet Oncol, 2019; NCT02039726). Additional support for the safety profile of quizartinib at the proposed dosing regimen (60 mg QD with a 30-mg starting dose) is provided by a pooled analysis of over 600 patients with R/R AML.

Methods: We pooled data from four studies: one phase 3 (QuANTUM-R), two phase 2, (ACC220-002 and 2689-CL-2004; Cortes, et al. Lancet Oncol, 2018; Cortes, et al. Blood, 2018), and one phase 1 (CP0001: only patients assigned to continuous daily dosing regimens are included in this analysis; Cortes, et al. J Clin Oncol, 2013) to provide an integrated safety summary of quizartinib monotherapy for the treatment of R/R AML. Treatment-emergent adverse events (TEAEs), on-treatment deaths, and adverse events of special interest (AESIs; QT prolongation and potential ventricular arrhythmias, hepatic disorders, and sequelae of cytopenias such as infections and bleeding) with quizartinib were analyzed.

Results: The pooled data set included 673 patients; 51% were male, and median age was 59 years. Thirty-eight patients were assigned to quizartinib 30 mg, 277 to 60 mg, and 358 to >60 mg up to 300 mg. Overall, median treatment duration was 79 days (range, 1-1296 days) and was longest in the 60-mg dose group (95 days) vs the >60-mg (70.5 days) and 30-mg (66 days) groups. The overall TEAE profile was consistent with the results from the phase 3 QuANTUM-R study. Most on-treatment deaths (215 of 599 evaluable patients [36%]; defined as taking place between the first dose and ≤30 days after the last dose) were attributed to AML disease progression (130/599 [22%]), followed by TEAEs (83/599 [14%]), which were predominantly respiratory tract infections and events related to sepsis. TEAEs leading to discontinuation of quizartinib occurred in 173/673 patients (26%). In the 60-mg dose group (quizartinib proposed dosing regimen), the only TEAE associated with discontinuation in >2% of patients was pneumonia (6/277 patients [2%]). The most frequently reported grade ≥3 TEAEs were febrile neutropenia (240/673 [36%]), anemia (188/673 [28%]) and thrombocytopenia (182/673 [27%]) in the hematologic category and pneumonia (119/673 [18%]) and sepsis/septic shock (124/673 [18%]) in the nonhematologic category (Table 1A). In the 60-mg dose group, the most frequent AESI was infection (210/277 [76%]; Table 1B). Epistaxis and petechiae, mainly grade 1/2, were the most frequently reported hemorrhage TEAEs. TEAEs in the hemorrhage category occurred more frequently in the >60-mg dose group than the 60-mg dose group (215/358 [60%] and 136/277 [49%], respectively). The most frequent serious hemorrhage TEAEs were gastrointestinal hemorrhages (15/673 [2%]) and intracranial hemorrhage (10/673 [2%]). QTcF prolongation >500 ms (grade 3) occurred in 75/673 patients (11%), mostly in those receiving quizartinib >60 mg (n = 64) (Table 1C). In the 60-mg dose group, QTcF prolongation >500 ms occurred in 9/277 patients (3%). The median time to onset of QTcF prolongation >500 ms was shorter in the >60-mg dose group than in the 60-mg dose group (9 and 46 days, respectively). Arrhythmias potentially related to QTcF prolongation were infrequent; one event of torsade de pointes, and one event of fatal cardiac arrest (both at doses >60 mg) were observed. No dose effects were seen with hepatic disorders, cardiac arrhythmias, or cardiac failure AESI categories.

Conclusions: The overall safety profile of quizartinib in this R/R AML pooled analysis is consistent with that observed in QuANTUM-R. A reduction in the incidence of QTcF prolongation was noted with lower doses of quizartinib (30 or 60 mg vs >60 mg). There was also a reduced incidence of gastrointestinal symptoms, infections, and bleeding at lower doses of quizartinib (30 or 60 mg vs >60 mg). Results from this pooled analysis demonstrate that quizartinib is well tolerated at the proposed dosing regimen (60 mg QD with a 30-mg starting dose) in patients with R/R AML.

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