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 (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.