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Monitoring Therapy in Chronic Myeloid Leukemia

Summary & Participants

A wide range of laboratory tests is used to monitor a patient's response to therapy for chronic myeloid leukemia. Listen to experts explain the tests and their range of sensitivity.

Medically Reviewed On: July 04, 2008

Webcast Transcript

ANNOUNCER: Treatment of chronic myeloid leukemia begins with bringing blood counts back to normal.

BRIAN DRUKER, MD: When a person is diagnosed with CML, they often will have as many as one trillion leukemia cells. Their white count is 5 to 50 times the upper limit of normal. If we can lower their blood counts to normal, we say that that's a complete hematologic response.

ANNOUNCER: Several drugs can normalize blood counts, but that doesn't mean the disease is under control. Doctors also try to reverse the underlying disease process. In order to monitor a patient's progress, doctors must be able to determine the percentage of white blood cells containing the underlying genetic abnormality.

MOSHE TALPAZ, MD: This disease has a hallmark, which is the presence of an abnormal chromosome also known as the Philadelphia chromosome. What happens in this chromosome abnormality is a phenomenon that we call translocation, a transition of a piece of a chromosome from chromosome 9 to chromosome 22 and from chromosome 22 to chromosome 9. And, as a consequence, if we look at the chromosomes under the microscope, we see particularly a deletion in the long arm of one of chromosome 22.

ANNOUNCER: Using a microscope to count white blood cells with the Philadelphia chromosome is called cytogenetic testing.

STEPHEN O'BRIEN, MBChB, PhD: A cytogenetic test is almost always done in a sample of bone marrow. So this is usually taken through a needle from the back of the pelvis, 1 or 2 milliliters, like a teaspoon full of marrow, is taken, put into a test tube, sent off to the lab and the cells are then cultured or grown. And, as they divide, you can see all the chromosomes in those cells and we're looking for this very small, this minute chromosome 22: the Philadelphia chromosome.

ANNOUNCER: It's not a very sensitive technique, because the standard sample is not very large.

NEIL SHAH, MD: One of the limitations of standard cytogenetic testing is we're only looking at twenty cells. And, so, really, to register a positive, you have to have at least 1 out of 20, or 5 percent, of the cells having the abnormal translocation. We know that patients start with an enormous burden of leukemic cells and less than 5 percent remaining could still mean a substantial number of cells in the body harboring this translocation.

ANNOUNCER: A more sensitive technique of identifying white blood cells with the Philadelphia chromosome is called fish, or fluorescence in situ hybridization.

NEIL SHAH, MD: This method allows a cytogeneticist to rapidly assess 500 cells for the presence of the translocation and if 1 is positive out of the 500, obviously that's a much greater sensitivity of this test than 1 out of 20 with standard cytogenetics.

ANNOUNCER: And if testing by fish reveals no Philadelphia chromosomes, doctors order even more sensitive testing.

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