Abstract
Extramedullary relapse of acute myeloid leukemia (AML) is a relatively common occurrence, with the FMS-like tyrosine kinase 3 (FLT3) mutation being a significant risk factor. While gilteritinib is approved for treating relapsed/refractory FLT3+ AML, its effectiveness in extramedullary relapse is still not well established. We report the case of a 69-year-old woman diagnosed with therapy-related nucleophosmin-1 (NPM1) and FLT3-internal tandem duplication (FLT3-ITD) positive AML. She was initially treated with induction and consolidation therapy using CPX-351 (liposomal daunorubicin plus cytarabine) and subsequently received off-label azacitidine maintenance. Although she achieved complete remission with persistent measurable residual disease, 19 months later she experienced an isolated breast relapse of FLT3-ITD+ AML. The patient was treated with single agent gilteritinib, which led to a rapid and sustained complete regression of the breast nodule, maintained after 44 courses of treatment. This case demonstrates that target therapy with gilteritinib can be an effective option for isolated extramedullary relapse of FLT3-ITD+ AML.