Translocation (3;21) in Philadelphia chromosome-positive chronic myelogenous leukemia prior to the onset of blast crisis.

Two female patients in the chronic phase of CML were found to have, in addition to t(9;22), a new karyotypic abnormality--t(3;21)(q26;q22)--present in bone marrow cells. At diagnosis, this abnormality was observed in a small number of marrow cells in both patients, and as the disease progressed in patient 1, the percentage of cells showing t(3;21) was increased, reaching 100% as the transformation to blast crisis occurred. These observations suggest that t(3;21) may represent a new and rare nonrandom rearrangement which may be identified prior to the onset of blast crisis.