Gilteritinib in Isolated Breast Relapse of <b><i>FLT3</i></b> Positive Acute Myeloid Leukemia: A Case Report and Review of Literature

Extramedullary relapse of acute myeloid leukemia (AML) is not a rare event, and the FMS-like tyrosine kinase 3 (<i>FLT3</i>) mutation is a well-known risk factor. Gilteritinib is approved for relapsed/refractory <i>FLT3</i>+ AML, but its efficacy in extramedullary relapse is still undefined. Here, we present the case of a 69-year-old woman with therapy-related nucleophosmin-1 and <i>FLT3</i>-internal tandem duplication (<i>FLT3</i>-ITD) positive AML treated with induction and consolidation with CPX-351 (liposomal daunorubicin plus cytarabine) followed by off-label azacitidine maintenance who obtained a complete remission (CR) with persistent measurable residual disease. After 19 months of CR, she experienced an isolated breast relapse of <i>FLT3</i>-ITD+ AML. She was started on single-agent gilteritinib, resulting in a rapid and persistent complete regression of the breast nodule. Targeted therapy with gilteritinib for relapsed/refractory <i>FLT3</i>-ITD+ AML can be effective in isolated extramedullary relapse.