Philadelphia (Ph) chromosome-positive chronic myeloid leukaemia relapsing as Ph-negative leukaemia after allogeneic bone marrow transplantation

Two patients with Philadelphia chromosome-positive (Ph+) chronic myeloid le ukaemia (CML) relapsed 1.5 and 5 years after allogeneic bone marrow transpl antation (BMT). Although the leukaemias were of recipient origin, t(9;22) c ould no longer be detected using conventional cytogenetics/fluorescence in situ hybridization or molecularly. Both patients responded to immunotherapy with donor lymphocytes/peripheral blood stem cells, although one patent ul timately relapsed again. These patients were similar to the occurrence of P h- leukaemias previously described in Ph+ CML after treatment with interfer on or autologous BMT, and might be relevant in the pathogenesis and monitor ing of treatment after BMT in CML.