Misleading cytogenetic evidence of relapse in donor cells after allogeneic bone marrow transplantation corrected by fluorescent in situ hybridization.

he possibility of a leukemic relapse in donor cells after allogeneic bone marrow transplantation (BMT) has been recognized since 1971, and it is usually demonstrated by means of karyotypic or molecular studies. This phenomenon has also been reported in chronic myelogenous leukemia (CML). Recently, FISH (fluorescent in situ hybridization) analysis has been employed to characterize hematopoietic cells in mixed chimeras, to obtain further evidence about the suspected donor origin of leukemic relapse after BMT, and even to demonstrate the donor origin of secondary neoplasms after solid allografts. We report here the case of a transplanted patient with CML, in whom FISH analysis allowed us to disprove a suspected leukemic relapse in donor cells that was suggested by conventional cytogenetics. Case report A 30-year-old female was diagnosed as having Ph1-negative, bcr/abl-positive (b2a2, p210) CML in October 1992. The patient was treated effectively with hydroxyurea, followed by a-interferon until April 1993, when she successfully underwent BMT from a matched male sibling. In April 1994, the patient relapsed with morphological and immunological features of common acute lymphoblastic leukemia. The growth fraction of leukemic cells, as determined using the APAAP technique and Ki67 monoclonal antibody, was found to be extremely low (< 1%). The blood group was still that of the donor. In this phase, repeated karyotype analyses of marrow cells (blasts 95%) demonstrated the presence of only six evaluable normal male (46, XY) metaphases, thus suggesting the possibility of a relapse in the donor cells.