A summary of cytogenetic studies on 534 cases of chronic myelocytic leukemia in Japan

Application of cytogenetics in neoplastic diseases

This review will concern itself with the application of cytogenetic findings in neoplastic diseases. This application can be divided into two general categories: practical and theoretical. The practical applications reside in utilizing karyotypic changes, particularly in leukemias and lymphomas, not only for diagnostic purposes but also for predicting response to therapy and prognosis. This is especially evident in the various acute nonlymphocytic leukemias and in most of the acute lymphoblastic leukemias. Thus, a definite correlation exists between the cytogenetic findings and the various clinical, laboratory, and cytologic parameters of most of the leukemias. Undoubtedly, these leukemias will ultimately be classified and defined more in terms of their cytogenetic aspects than any other. Though the application in lymphoma is not at the same level as that in leukemia, developments in that field certainly indicate a similar utilization of the cytogenetic findings in these diseases. The presence or absence of a Ph1 chromosome in a chronic myelocytic leukemia has been utilized widely, not only in the diagnosis but also in the predictability of response; the cytogenetic findings have also been utilized in predicting the blastic phase of disease. The list of specific chromosome changes in various solid tumors is of a lesser number, but significant developments indicate that the applicability of chromosome changes in these diseases will, also, be established in the near future. The application of chromosome findings to theoretical aspects of malignancy has assumed an important place recently in the demonstration that so-called oncogenes (or proto-oncogenes) are located or associated with areas of human chromosomes in which breaks and translocations are involved. Thus, it appears that chromosome changes in human malignancy, once their specificity is established, are important parameters in the clinical and theoretical aspects of the disease. A discussion will also be given on primary vs. secondary chromosome changes and their significance in the biology and behavior of the malignancy.

Is the chromosomal region 9q34 always involved in variants of the Ph1 translocation?

Six variants of the Ph1 translocation are described. The clinical diagnoses were chronic myeloid leukemia (CML) in 5 cases (patients 1-5) and acute lymphocytic leukemia (ALL) in patient 6. Three Ph1 variants were clear complex translocations, involving chromosomes #9, #22, and a third chromosome, i.e., #16, #11, or #14. The other three Ph1 variants appeared as "simple" translocations between chromosome #22 and chromosome #19, #4, or #12 when G- or Q-banding were used. When studied with high resolution R-banding, a small deletion of the terminal part of one chromosome #9 was visible, strongly suggesting that these variants were also complex translocations, i.e., t(9;19;22)(q34;p13;q11),t(4;9;22) (p16;q34;q11), and t(9;12;22)(q34;p13;q11). In the latter two cases, using in situ hybridization techniques, we demonstrated the presence of c-abl sequences on the Ph1 chromosome. This proved the involvement of 9q34 in these two variants. Our proposal is that most, and probably all, variants of Ph1 are complex translocations involving part of 9q34 and that the conjunction of a specific region of 22q11 with a specific segment of 9q34 (carrying the c-abl protooncogene) is essential for the development of Ph1 + CML.