Successful treatment with gilteritinib for isolated extramedullary relapse of acute myeloid leukemia with FLT3-ITD mutation after allogeneic stem cell transplantation.

Acute myeloid leukemia (AML) harboring Fms-like tyrosine kinase 3 (FLT3) internal tandem duplication (ITD) mutation is associated with shorter remission and higher relapse risk. Several FLT3 inhibitors have been used in clinical trials, but their efficacy in extramedullary disease remains unclear. In the present case, a 56-year-old man was diagnosed with FLT3-ITD mutated AML. Due to bone marrow relapse during consolidation therapy, he underwent salvage therapy and a myeloablative conditioning regimen, followed by peripheral blood stem cell transplantation (PBSCT) from a HLA-matched related donor. Acute graft-versus-host disease (GVHD) did not develop, and complete donor chimerism was confirmed on days 27 and 96 after PBSCT. On day 180, he experienced extensive chronic GVHD and had several subcutaneous tumors in his body, which were diagnosed as myeloid sarcoma by pathological examination. We considered this to be a case of isolated extramedullary relapse, as his bone marrow had maintained complete donor chimerism. Treatment with etoposide and ranimustine produced no effect, and tumor progression continued. We started administration of gilteritinib, a FLT3/AXL inhibitor, after identifying the FLT3-ITD mutation in the tumor. Subsequently, there has been a remarkable regression of the tumors. Gilteritinib can be effective in isolated extramedullary relapse after allogeneic stem cell transplantation.