Tracking Treatment Progress: ... Video Transcript

Participants

, John M. Goldman MD, Steve MacKinnon MD, Stephen O'Brien MBChB, PhD

Summary

Tracking faulty chromosomes is routine for people with chronic myeloid leukemia. Listen as experts explain why sophisticated laboratory tests that count chromosomes are important in determining how well a patient is responding to therapy.

Webcast Transcript

ANNOUNCER: Chronic Myeloid Leukemia is a cancer of the blood. The disease starts with a faulty gene, formed when the ends of two normal chromosomes break, and the wrong pieces join together.

STEVE MACKINNON, MD: Well, in chronic myeloid leukemia there is a cytogenetic or chromosomal abnormality that's called the Philadelphia chromosome, and that is a translocation between chromosome 9 and chromosome 22, and that is characteristic of this disease.

ANNOUNCER: The defect leads to the uncontrolled growth of white blood cells. There's only one cure, one sure-fire way to rid the body of all cells containing the Philadelphia chromosome. Unfortunately, it carries a high risk.

JOHN GOLDMAN, MD: Ideally, the goal of therapy for patients for CML must be cure-total and permanent eradication of the disease. The only way that we can currently do that is with an allogenic stem cell transplantation. In other words, bone marrow transplantation, which can be highly effective in curing the disease, but which remains dangerous today. When the transplant goes wrong, people can die as a consequence of a failed transplant.

ANNOUNCER: Bone marrow transplants are usually performed only when patients are young, have no other serious medical problems, and when a donor with very similar tissue is available. Even when transplants are not feasible, there's plenty that can be accomplished with medical therapy.

JOHN GOLDMAN, MD: If you don't plan a transplant for an individual patient, then the first and easiest goal of therapy is to restore the blood count to normal, shrink a patient's enlarged spleen and remove all the symptoms they had attributable to a high white cell count. The next goal would be to reduce the measurable amount of leukemia in their body, measuring the leukemia with cells carrying the Philadelphia chromosome in the blood, and cells carrying the Philadelphia chromosome in the bone marrow.

ANNOUNCER: Bringing a patient's blood counts back to normal-what's called a good hematologic response-is relatively easy. It's usually achieved with a chemotherapy drug called hydroxyurea.

JOHN GOLDMAN, MD: Hydroxyurea is a valuable drug because a patient who presents with symptoms due to chronic myeloid leukemia may have sweats and weight loss and a big spleen that could be painful, and hydroxyurea reverses all those features within two or three weeks. It does not, however, reduce the proportion of leukemia cells in a patient's bone marrow, and it probably contributes nothing towards cure. Doctors turn to other drugs to reduce the number of cells containing the Philadelphia chromosome, particularly interferon and Gleevec. Doctors also order frequent lab tests on samples of marrow or blood cells, to check the result-what's called the "cytogenetic" response. Monitoring that response is important, for doctors believe the fewer cells with the Philadelphia chromosome, the longer a patient may live.

STEVE MACKINNON, MD: The status of the Philadelphia chromosome following treatment for CML is important because previous studies have shown that patients who get a major chromosomal or complete chromosomal response to therapy have better survival.

STEPHEN O'BRIEN, MBChB, PhD: Cytogenetic responses in CML are classified as either a complete response, which means there are no detectable Philadelphia chromosomes out of 30 cells usually that are analyzed. A so-called partial cytogenetic response means that there are less than 35% of cells Philadelphia-positive.

ANNOUNCER: Interferon, a standard therapy, brings about a complete cytogenetic response in 10 to 20 percent of patients.