The first connection between cancer and a patient’s genome was documented by Peter Nowell and David Hungerford when they identified a unique chromosome in the metaphase spread of 7 patients diagnosed with chronic myeloid leukemia (CML). In 1973, renowned cytopathologist Janet Rowley determined that this chromosome is part of a chromosomal translocation between chromosome 9 and chromosome 22. Further delineation of this translocation showed that the gene ABL1, normally located on chromosome 9, is translocated to the Philadelphia (Ph+) chromosome in patients with CML. ABL1 was found to be located downstream of a specific genetic region in each patient, and this region became known as the BCR, or “breakpoint cluster region.” The BCR-ABL1 translocation found in patients with CML creates a constitutively active tyrosine kinase necessary for cellular transformation.
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