Tracking Treatment Progress: ... Video Transcript

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Gleevec, or imatinib, which is a much newer drug, attacks CML in a different way. And it brings about a complete cytogenetic response more often, according to results from an ongoing clinical trial.

STEPHEN O'BRIEN, MBChB, PhD: The latest data has shown there are huge differences in cytogenetic response on patients on imatinib against interferon. So the response rate, for example, on complete eradication of the Philadelphia chromosome on imatinib is about 75%, and with interferon and the other drug used in the trial, ARA-C, it's only about 14%. When lab tests show no Philadelphia chromosomes, the message for the patient is good. But it's not the end of the story.

JOHN GOLDMAN, MD: The doctor then happily tells the patients, "You've reached a complete chromosomal remission, and that's a very good target, and should indicate that you're going to live a lot longer than if you had not achieved a complete chromosomal remission." Then I think the perceptive patient may say, "Does that mean that there is no evidence of leukemia in my body?" And the doctor will honestly reply, "No, if I do a molecular test, the so-called PCR test, I may still find evidence of leukemia in your body." "So I'm not cured yet?" "No, you're not entirely cured."

Standard cytogenetic testing samples just 20 or 30 cells at a time. A newer cytogenetic technology, called fluorescence in situ hybridization can check many more. But the most sensitive test-called PCR-uses molecular techniques to check on hundreds of thousands or millions of cells at a time.

STEVE MACKINNON, MD: The cytogenetic test, you're looking down a microscope at chromosomes of individual cells. In the molecular test or the PCR test, you can look at large numbers of cells at once, and you can amplify up the genetic material using a polymerase chain reaction test. And this can amplify a single copy of a gene many thousands and millions of times. So that even if there's only one cell in a million normal cells, you can see that following the PCR test. That sensitivity is important because doctors believe CML can bounce back if even a few cells with the Philadelphia chromosome remain in the body.

JOHN GOLDMAN, MD: I guess we think that the continuing presence of a very small number of leukemic cells does mean that if you relax therapy, the leukemia could come back in its full form over a number of months or years. The simplistic way of thinking about cure is to say that you're not cured until you've eradicated every single leukemia cell from a patient's body.

ANNOUNCER: A generation of treatment of CML rests on the discovery of the Philadelphia chromosome, and on lab tests that can detect it in a patient's body. As our understanding of CML deepens, so have monitoring techniques. No longer are doctors limited to counting flawed chromosomes under the microscope. Now they can rely on tests thousands of times more sensitive, ones that check at the molecular level for the presence of the bad gene responsible for most cases of the disease.

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