Specificity of the Philadelphia Chromosome

Abstract

The results of cytogenetic studies of the peripheral leukocytes taken from patients with chronic myelocytic leukemia and myeloid metaplasia are reported. In all 10 cases of chronic myelocytic leukemia in various stages of the disease, typical Ph1 chromosomes were identified, but in various proportions of the cells examined. The percentage of cells containing this abnormal chromosome varied from 27% to 100%. None of the metaphases examined in 8 patients with myeloid metaplasia showed the Ph1 chromosome, regardless of the clinical manifestation of the disease or the level of the leukocyte alkaline phosphatase. In patients with chronic myelocytic leukemia, two-day cultures of leukocytes gave better yields of the Ph1 chromosomes than did three-day cultures. This probably reflects the difference in the number of normal lymphocytes in mitosis at the time when the cultures were terminated. Morphological abnormalities of chromosomes were seen in 3 patients with CML whose peripheral blood leukocytes were cultured while the patients were receiving antileukemia therapy. It was concluded from these observations that the Ph1 chromosome is specific for chronic myelocytic leukemia and is absent in myleoid metaplasia. This finding may be of practical use in differentiating these two diseases especially when a bone marrow specimen is inadequate for cytogenetic studied.