Abstract
Gilteritinib is a selective FLT3 inhibitor approved for the treatment of relapsed or refractory (R/R) FLT3-mutated acute myeloid leukemia (AML) following ≥ 1 prior line of therapy. However, data on its effectiveness in later-line settings is limited. We conducted a multicenter, retrospective study including 171 adult patients with R/R FLT3-mutated AML who received gilteritinib as third-line or beyond between August 2017 and March 2024 across centers in Italy, Spain, the United Kingdom, and Turkey. The primary endpoint was overall survival (OS). Secondary endpoints included overall response rate (ORR), composite complete remission (cCR), duration of response. Among the 171 patients, 84% carried FLT3-ITD mutations and 26% had received ≥ 3 prior lines of therapy. The cCR rate was 28%, and ORR was 47%. Patients who were younger and presented with relapsed (vs. refractory) disease had better outcomes. Prior exposure to venetoclax or allogeneic hematopoietic stem cell transplantation (HSCT) was associated with inferior response. Gilteritinib enabled HSCT in 12% of patients. Median OS was 7.1 months (95% CI, 5.9-10.1), and in Cox-regression analysis was significantly improved among responders and those who underwent HSCT (median OS: 21.5 months; 95% CI, 12.8-NR). Prior venetoclax exposure was associated with shorter survival (5.7 months; 95% CI, 5.1-8.8). On multivariate analysis, previous exposure to venetoclax and FLT3 inhibitors was the strongest predictor of reduced response rates. Despite heavy pretreatment, gilteritinib retained clinically relevant activity in later-line R/R FLT3-mutated AML. Its use beyond second-line may serve as a bridge to HSCT in selected patients. Resistance mechanisms, particularly following venetoclax, remain a therapeutic challenge. These data support the continued use of gilteritinib beyond second-line and highlight the need for prospective studies to optimize sequencing strategies.