Dicentric isochromosome for the long arm of chromosome #17, dic i(17q), in a patient with chronic myelogenous leukemia (CML).

Cytogenetic studies in a 33-year-old male patient with chronic myelogenous leukemia of 7 years duration revealed a so-called i(17q) chromosome marker and other cytogenetic abnormalities during the early phase of blastic crisis which were not present at diagnosis. Careful morphologic examination of this marker using G- and C-banding techniques revealed it to be a dicentric chromosome with a very short intercentromeric area. The fact that the dicentric nature of this marker was not apparent with the conventional Giemsa stain emphasizes the usefulness of the C-banding technique in defining the origin of this important cytogenetic marker.