The cytogenetic follow-up of a case of refractory anemia with excess of blasts (RAEB) that rapidly evolved to acute myeloblastic leukemia (Ml-FAB type) is described. Bone marrow analysis at presentation revealed two chromosomally abnormal clones that shared an interstitial deletion of the long arm of chromosome 5 (5q−) and a terminal deletion of the short arm of chromosome 12 (12p-), but that differed from one another in the localization of a very similar segment of chromosome 17 (i.e. 17q11−12qter) on two clearly distinct karyotypic sites: 2q37 and 17q25. Fourteen percent of the metaphases examined bore the 2q+ marker and 38 the 17q+ marker; the remaining cells had a normal karyotype. A second study carried out 4 months later, at onset of the acute phase, revealed that the clone with normal karyotype had almost completely disappeared and that there had been an inversion in the ratio of the two abnormal cell populations. In the final study, made 1 month before death, the cells with t(2;17) had totally effaced the other cl
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