Isolated Extramedullary Relapse After Human Leukocyte Antigen-Matched Myeloablative Allogeneic Hematopoietic Stem Cell Transplantation in Acute Myeloid Leukemia Patients: Case Reports and Literature Review

•Isolated extramedullary relapse of acute myeloid leukemia after transplantation is a rare but dismal prognosis.•The common sites of isolated extramedullary relapse of acute myeloid leukemia are the central nervous system, skin, and lymph node.•Rare cardiac presentation of leukemia can occur.•Local and systemic leukemia treatment should be considered for isolated extramedullary relapse. Isolated extramedullary relapse (iEMR) of acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is rare and has a dismal prognosis. Among 67 patients with AML after allo-HSCT, iEMR and bone marrow relapse occurred in 6% and 20.9%, respectively, with a median time to relapse of 11.5 and 6.5 months, respectively. Here, we presented 4 iEMR-AML cases. Common relapse locations occurred in the central nervous system, skin, and lymph nodes. We also report a rare case of cardiac iEMR that responded to chemoradiotherapy. Two cases responded to local/systemic treatments, which resulted in prolonged survival. Another case had iEMR in the presence of chronic graft-versus-host disease. Bone marrow relapse occurring after iEMR was typical and found in three-fourths of the cases. In conclusion, iEMR-AML occurrence after allo-HSCT is not rare in Thai patients. Its unpredictability and lack of graft-versus-leukemia effect highlight the importance of monitoring EMR carefully and promptly providing treatments once it is detected.