ABSTRACT
<p><b>OBJECTIVE</b>To explore the role of monitoring sex chromosome chimeric status by fluorescence in situ hybridization (FISH) in the identification of leukemic extramedullary relapse and post-transplant lymphoproliferative disease (PTLD) in acute lymphocytic leukemia (ALL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT).</p><p><b>METHODS</b>Six ALL patients who received sex-mismatched allo-HSCT and manifested extravisceral lymphadenectasis or local lump were investigated. The sex chromosome chimeric status in tumor tissues and bone marrows (BM) were monitored by FISH, and EBV-RNA in the tumor tissues were detected by in situ hybridization (ISH).</p><p><b>RESULTS</b>The sex chromosomes in BM of all 6 patients were 100% donor-derived. Among the sex chromosome chimeric status of tumor tissues, three patients were mainly recipient-derived, and the percentage of sex chromosomes derived from recipients were 100%, 100% and 98.0%, respectively, and then they were diagnosed leukemic extramedullary relapse. The other 3 patients were donor-derived, the percentage was 98.5%, 96.0% and 91.5%, respectively, and were diagnosed PTLD. EBV-RNA and latent membrane protein (LMP-1) were positive in 2 patients with PTLD and negative in the other 4 patients. One patient with extramedullary relapse obtained partial remission, one with PTLD gained complete remission, and the others died eventually after therapy.</p><p><b>CONCLUSION</b>Monitoring the sex chromosome chimeric status by FISH is an effective method to distinguish leukemic extramedullary relapse from PTLD in ALL received sex-mismatched donor HSCT.</p>