A PHILADELPHIA-NEGATIVE CHRONIC MYELOID-LEUKEMIA WITH A BCR ABL FUSION GENE ON CHROMOSOME-9/

A 40-year-old man had chronic myeloid leukemia (CML) and an apparently normal karyotype. Fluorescence in situ hybridization with a BCR/ABL1- S probe, which is formatted to display a BCR/ABL fusion signal on chro mosome 22, gave a positive fusion signal on a chromosome 9. Therefore this patient has a BCR/ABL fusion gene on chromosome 9. The BCR/ABL1-D probe, formatted to display a fluorescent signal for both the recipro cal products of a 9/22 rearrangement, gave a positive fusion signal on the derivatives 9 and 22. These findings favor either a cryptic recip rocal exchange between BCR and ABL loci or the reversal of a Philadelp hia translocation. An insertion of BCR next to ABL is ruled out. The r everse-transcriptase polymerase chain reaction provided molecular evid ence that a typical CML chimeric product resulting from a fusion of BC R ex-on 2 with C-ABL exon II, a(2)b(2), is present. (C) Elsevier Scien ce Inc., 1998.