Leukemia Treatment Ineffective in Rare Cases

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A drug that is used to treat a rare form of leukemia may not fight the same disease in the central nervous system, according to researchers at University of Texas-Southwestern Medical Center at Dallas.

"The results were very unexpected," said Dr. Robert Ilaria Jr., assistant professor of internal medicine and molecular biology.

The Food and Drug Administration (FDA) approved STI-571 (Gleevec®) nearly two years ago to treat patients with chronic myelogenous leukemia (CML). CML is a relatively uncommon form, with about 5,000 new cases diagnosed each year in the U.S. The drug blocks signals within cancer cells and prevents a series of chemical reactions that cause the cell to grow and divide.

Gleevec® is a chemical inhibitor of the Bcr/Abl tyrosine kinase, a dysregulated enzyme that is believed to cause leukemia. The drug prevents Bcr/Abl from stimulating the white blood cells to grow and overproduce, especially blast (immature) cells.

Although not an inherited disease, CML has a genetic component. It is caused by an abnormal joining in bone marrow cells of deoxyribonucleic acid (DNA) sequences from two chromosomes that form an altered chromosome (the Philadelphia chromosome), which results in an overproduction of white blood cells. CML usually develops slowly, although it can progress to a fast-growing "accelerated phase."

"So far in humans, it appears that only CML cases that progress to lymphoid blast crisis (a marked increase in immature cells) or patients with Philadelphia chromosome-positive ALL are at risk for CNS leukemia," he said. "Such patients will require CNS treatments with other chemotherapeutic drugs besides Gleevec®."

Animal experiments using Gleevec® showed great promise, but did not translate into humans.

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