In situ hybridization ascertains the presence of a translocation t(6;11) in an acute monocytic leukemia.

In situ hybridization was performed in a case of acute monoblastic leukemia (FAB type M5b) with a rearrangement of the long arm of chromosome 11. Cytogenetic analysis after R- and G-banding showed an apparent deletion of 11q with a breakpoint at 11q23, and a translocation t(6;11) was suspected in certain metaphases. In situ hybridization with a biotinylated cosmid probe hybridizing at 11q25 confirmed the translocation t(6;11)(q27;q23). Use of nonradioactive in situ hybridization techniques for more precise characterization of chromosomal rearrangements in malignant cells is emphasized.