The Philadelphia chromosome. Considerations based on studies of variant Ph translocations.

The nature of the Philadelphia (Ph) translocation and the process of its formation were studied by attempting various chromosome banding analyses of variant Ph translocations among 210 patients with Ph-positive chronic myelocytic leukemia examined at the National Institute of Radiological Sciences, Chiba. The following assumptions could be drawn from the results of the analyses: 1) The involvement of specific regions of chromosomes #9 and #22, q34 and q11, respectively, is an indispensable condition of the Ph translocation. 2) The so-called variant Ph translocations are all complex and are derived from a standard Ph translocation. 3) The Ph translocations, both standard and complex ones, are not always stable. The complex translocations are subject to further chromosome evolution, as is the conversion of the standard translocation to complex translocations. There seems to be no fundamental difference between the standard and complex Ph translocations, with the latter being merely a more progressed form of the former. Analyses at the molecular level of the same cases employed in this study are yielding results that support the above assumptions.