9q34 rearrangements in BCR/ABL fusion-negative acute lymphoblastic leukemia.

The t(9;22)(q11.2;q34) translocation is found in a subset of acute lymphoblastic leukemia (ALL). The presence of this translocation involving the fusion of BCR/ABL genes represents a poor prognostic group. Because of the importance in detecting t(9;22) in ALL patients and because occasionally a cytogenetically cryptic BCR/ABL fusion is detected with fluorescence in situ hybridization (FISH), our laboratory routinely performs BCR/ABL FISH tests on all newly diagnosed ALL patients. In the past year, 25 consecutive, newly diagnosed, untreated ALL cases were analyzed. We report the cytogenetics and FISH findings of three cases containing a rearranged 9q34 region with an intact BCR (22q11.2) region and an absence of the BCR/ABL fusion. A split ABL signal representing a translocation of the 9q34 region with chromosome segments other than 22q11.2 (BCR) was observed in 3 cases. Two of these patients were 3 years old; one was 21 at the time of diagnosis. A split ABL FISH signal without the involvement of BCR does not represent a t(9;22) translocation, and prognostic implications of this apparent subgroup of ALL cases have not been determined. Cytogenetic, pathologic, and clinical aspects of these three cases are presented.