Molecular markers may help to redefine relapse for leukemia patients

December 04, 1999

Fred Hutchinson Cancer Research Center Researchers Present Results of Study Using Molecular Markers to Detect Residual Disease in Leukemia Patients

NEW ORLEANS, DEC. 5, 1999 -- Fred Hutchinson Cancer Research Center researchers are working to better understand the meanings of remission, relapse and cure by using molecular markers to detect minimal residual disease (MRD) in patients who have undergone treatment for leukemia. Results from a study looking at the significance of MRD in long-term Chronic Myelogenous Leukemia (CML) survivors will be presented at the 41st annual American Society of Hematology meeting Dec. 3-7 in New Orleans, La.

The team, led by Jerald Radich, M.D, a member of the Hutchinson Center's Clinical Research Division and Program in Genetics, are using a DNA fingerprinting technique known as polymerase chain reaction (PCR) to detect a single leukemia cell among 100,000 to 1 million normal cells. They use this super-sensitive molecular technique to detect MRD or trace amounts of leukemia cells in a patient's blood or bone marrow. The goal is to detect which patients, who appear to be in remission by conventional methods, still harbor disease and will eventually relapse. The long-term goal is to initiate secondary treatment at the earliest signs of relapse.

Most conventional methods of determining remission or relapse involve a microscopic examination by a pathologist. This technology can, however, only detect cancer when the number of cancerous cells in the blood reaches a level of about one per 20 cells. PCR, a Nobel Prize-winning technology, essentially takes snippets of genetic material and copies them over and over until there is a large enough quantity for researchers to "see" and analyze.

In CML, a genetic rearrangement known as the Philadelphia Chromosome occurs when a pieces of chromosome 22 and chromosome 9 exchange places. At the genetic level, this rearrangement results in part of the bcr gene from chromosome 22 linked with part of the abl gene from chromosome 9. This juxtaposition of bcr and abl in CML cells creates a unique genetic "fingerprint" in CML cells not found in normal cells. This unique genetic target can be amplified by PCR at a sensitivity of detecting one CML cell in a background of a million normal cells.

Radich's laboratory team initially performed a series of examinations of blood and marrow cells from 342 CML patients at various intervals after marrow transplantation. They found that patients with detectable bcr-abl by a qualitative assay (positive or not for bcr-abl detection) between 6-12 months after transplant carried a 42 percent greater risk of relapse. That compared to only a 3 percent increased risk for those patients whose PCR tests showed no cancerous cells. This study laid the groundwork for intervention trials in bcr-abl positive patients at the Hutchinson Center and the University of Washington.

The current study presented at ASH investigated the prevalence and significance of MRD in CML patients after years from transplant. They found that approximately 25% of patients had evidence of bcr-abl at some time following 18 months to 10 years following transplant. Patients found to be bcr-abl positive had approximately a 20% probability of relapse. The next challenge was to develop a fast and reliable quantitative method so that the actual levels of disease burden - and the trends of disease burden over time - could be studied. The Radich lab used the promising technique of "real time" PCR, using fluorescent markers and laser detection pioneered by Applied Biosystems. In this technique, fluorescent tags attached to the PCR primers light up when passed before a laser beam connected to a computer that calculates the accumulation of the target versus PCR cycle times. Based on the results, researchers can produce an estimate of total quantity of the cancerous cells. The results suggested that such quantification could discriminate those patients with increasing disease load versus those with declining or stable CML. It is hoped that in the future these methods can pick those patients who, while appearing to be cured of disease, have small but increasing disease activity, and who might benefit from early therapeutic intervention.
The Fred Hutchinson Cancer Research Center is an independent, nonprofit research institution dedicated to the development and advancement of biomedical technology to eliminate cancer and other potentially fatal diseases. Recognized internationally for its pioneering work in bone-marrow transplantation, the Center's four scientific divisions collaborate to form a unique environment for conducting basic and applied science. The Hutchinson Center is the only National Cancer Institute-designated comprehensive cancer center in the Pacific Northwest. For more information, visit the Center's Web site at < >

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Fred Hutchinson Cancer Research Center

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