Isochromosome 17q in Ph-negative chronic myelocytic leukemia.

No Ph chromosome was found in three clinically suspected chronic myelocytic leukemia (CML) patients, although one had metaphases with trisomy 13. An isochromosome of the long arm of chromosome 17 [i(17q)] was found in these patients when two of them were in acute blastic crisis (ABC) and the other in an early stage of transformation. Although an i(17q) is frequently seen in ABC of Ph-positive CML, it is rarely reported in Ph-negative CML. The finding of an i(17q) chromosome in Ph-negative CML appears to indicate, as in Ph-positive CML, that the disease is transforming into ABC. A series of cytogenetic studies in this group of patients may possibly aid in predicting the patients' pending ABC and may also lead to understanding the pathogenesis of ABC.