Cytogenetics and oncogenes

There is abundant evidence that leukemia arise through somatically acquired genetic changes. Familial or congenital predisposition is rarely involved. These genetic changes are often visible as chromosomal aberrations. Molecular analyses of the DNA sequences rearranged in leukemia has demonstrated the presence of cellular oncogenes which are modified (fused, mutated, truncated) by the specific translocations. This results in a disturbance of the delicate balance between proliferation and differentiation and constitute a major step towards cell transformation. Some of these genetic rearrangements have been analyzed in depth, but the exact defect that causes leukemia is often not yet understood. Meanwhile these studies have increased our knowledge of normal cell proliferation and differentiation and provided us with new tools for diagnosis and for developing more specifically targeted treatment. An example would be the production of antibodies that recognize specifically the new chimeric proteins. Oncogenesis is a complex and multiple step process that proceeds by acquisition of successive genetic insults. The different steps do not necessarily occurs following a predetermined order, although some secondary changes are preferentially induced by a given first mutation. In leukemia, sequential changes in karyotype are well documented but molecular makers for tumor progression have not yet been systematically investigated. This is one of our many challenges for the future.