Unusual clinical course and acquisition of del(11)(q23) in second lymphatic blastic phase of a Ph-positive chronic myeloid leukemia

We describe unusual clinical and cytogenetic findings of a 29-year-old fema le with a Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (C ML), who showed a mosaic of apparently normal cells and cells bearing the c lassical t(9;22)(q34;q11) during the first lymphatic blastic phase (BP). Th e second lymphatic BP developed 10 years later. In addition to the t(9;22), which was defected in all metaphases, a del(11)(q23) was identified as a s ubclonal change in 4 of 25 metaphases. Fluorescence in situ hybridization ( FISH) analysis using a chromosome 11-specific library probe and a probe cov ering the breakpoint cluster region of the MLL gene revealed hybridization signals of both probes on the normal and the deleted chromosome 11, indicat ing that the breakpoint on chromosome 11 occurred telomerically to the brea kpoint cluster region of the MLL gene. Chemotherapeutic treatment resulted in reconstitution of the chronic phase with persistence of the Ph transloca tion as the sole chromosomal abnormality. (C) Elsevier Science Inc., 1999. All rights reserved.