OBJECTIVETo 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).

METHODSSix 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).

RESULTSThe 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.

CONCLUSIONMonitoring 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.