In 1972, Dr. Janet Rowley discovered the first consistent chromosome translocations associated with cancer — a finding that helped to demonstrate that cancer was a genetic disease. For her work, she was awarded the coveted Lasker Award and the National Medal of Science in 1998.
In 1962, Rowley began to study the chromosomes of patients with leukemia. For the next decade she labored over the microscope, looking for consistent chromosome abnormalities amid the seeming genetic chaos of leukemic cells.
The first such abnormality had just been reported by Peter Nowell and colleague David Hungerford, who found that patients with chronic myelogenous leukemia (CML) had an abnormally small chromosome 22 in their tumor cells, which they called the "Philadelphia" chromosome.
The next big step came in the early 1970s when geneticists perfected the art of chromosome "banding," a new way of visualizing segments of chromosomes with great precision. This improved resolution allowed Rowley to discover that chromosomes from leukemic cells not only lost genetic material, they sometimes exchanged it. Early in 1972, Rowley discovered the first such "translocation," an exchange of small pieces of DNA between chromosomes 8 and 21 in patients with acute myeloblastic leukemia.
Later that same year, she found that Nowell and Hungerford's "Philadelphia" chromosome was also the result of a translocation. In patients with CML, a crucial segment of chromosome 22 broke off and moved to chromosome 9, where it did not belong. At the same time, a tiny piece of chromosome 9, which included an important cancer-causing gene, had moved to the breakpoint on chromosome 22. Because of this transfer from one chromosome to another, important genes that regulated cell growth and division were no longer located in their normal position on the chromosome. This provided critical evidence that cancer was a genetic disorder.
Rowley and her colleagues subsequently identified several other chromosome translocations that were characteristic of specific malignancies, such as the 14;18 translocation seen in follicular lymphoma, and the 15;17 translocation that causes acute promyelocytic leukemia (APL). Quickly picking up on her lead that specific translocations defined specific forms of cancer, scientists around the world joined the search for chromosomes that either exchanged genetic material or in some cases lost it altogether in a process known as a "deletion." Others used the translocations as road maps to narrow the search for specific genes that were disrupted by chromosome damage, thus opening up the current era of cancer genetics.