Chromosome examinations were performed on bone marrows from 88 patients with Ph1-positive chronic myelocytic leukemia (CML). As a group, Ph1-positive CML patients with some cytogenetically normal cells in the marrow survived much longer than those whithout such cells in their marrow. The survival for patients whose first bone marrow exhibited only metaphases with a Ph1 and other karyotypic abnormalities was significantly shorter than that for patients whose marrow exhibited only metaphases with

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... a Ph1 and an otherwise normal karyotype or patients whose marrow contained both categories of cells. The shorter the interval between the diagnosis of CML and the first chromosome examination, the greater the frequency of karyotypically normal cells in the bone marrow. Karyotypic progression in CML was a common phenomenon, whereas a reversion was very rare. On the basis of the findings obtained, the early diagnosis and treatment of CML are indicated, both possibly being helped by the chromosomal findings in the marrow. Furthermore, a combination of the chromosomal data and the marrow cell differential may serve as an important prognostic index in CML.