All forms of leukemia have similar symptoms, but the treatments differ. Chronic myelogenous leukemia (CML) is caused by a defect in one specific gene on chromosome 22. When this chromosome appears shorter than normal, it is called the Philadelphia chromosome. Chronic leukemia develops and progresses slowly at first, so that 20 to 40 percent of patients have no symptoms when they are first diagnosed based on a routine white blood cell count. However, the untreated disease typically progresses to an accelerated phase.
Dr. Jerry Avorn, a Harvard Medical School professor, describes research on treating CML as a milestone in pharmaceutical research. Most chemotherapy agents attack rapidly dividing cells in general, so that they kill a large number of healthy cells along with the malignant cells. Hair loss, nausea, and vulnerability to infection are well-known side effects of this class of drugs. “The holy grail of oncology research,” according to Avorn, is “blocking cancer cells preferentially without destroying normal ones, yielding a treatment that would cause many fewer side effects than conventional chemotherapy.”
Basic science researchers work to understand what specifically goes wrong with cancer cells to cause the aggressive and uncontrolled cell division. The Philadelphia chromosome was identified and linked with CML at the University of Pennsylvania. Further work at MIT, the University of California at San Francisco and at San Diego, the University of Chicago, and the Salk Institute produced important advances in understanding how the signaling protein BCR-ABL is involved in cancer. The Howard Hughes Medical Institute funded additional research in linking this protein to CML.
The result of these research efforts is a class of drugs called abl kinase inhibitors. The first-line treatment is Gleevec (imatinib), and has been successful in many patients. For patients who do not improve with this drug, alternatives include dasatinib (Sprycel) and nilotinib (Tasigna).
According to Reference 1, the only cure for CML is a transplant of stem cells, usually from bone marrow. Unfortunately, transplantation has its own risks and is considered a “fall back option”. With drug treatment, the 6 year-survival rate is reported as 88 percent. Reference 2 reports 5 year survival rates of 80 to 95 percent.
Research continues into further treatment options.
References:
1. von Bubnoff N et al, “Chronic Myelogenous Leukemia”, Dtsch Arztebl Int 2010; 107(7): 114-21.
2. Vardiman JW, “Chronic Myelogenous Leukemia, BCR-ABL1+”, Am J Clin Pathol 2009 Aug; 132(2): 250-60.
3. Jerry Avorn, M.D., “Powerful Medicines”, Vintage Books, 2004.
4. Gleevec web site:
http://www.gleevec.com/index.jsp
5. Other drug options:
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000429
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0000412
Linda Fugate is a scientist and writer in Austin, Texas. She has a Ph.D. in Physics and an M.S. in Macromolecular Science and Engineering. Her background includes academic and industrial research in materials science. She currently writes song lyrics and health articles.