This month marks the 30-year anniversary of the declaration of the "war on cancer," and although victory over the disease is years away, singular advances helped many cancer patients in 2001.

One of this year's most promising advances is a drug called Gleevec, now in use for chronic myelogenous leukemia (CML), a cancer of the white blood cells.

The Food and Drug Administration (FDA) this year approved Gleevec for three stages of CML: CML myeloid blast crisis, CML accelerated phase, and CML in chronic phase after failure of interferon treatment.

And, the drug is currently being studied for treatment of other cancers such as gastrointestinal stromal tumors (GIST), gliomas (brain tumors), and soft tissue sarcomas.

Gleevec, made by Novartis, is a new type of oral cancer drug that works by turning off an enzyme that causes cells to become cancerous and grow. Earlier this year the FDA said in its announcement that Gleevec substantially reduces the level of cancerous cells in the bone marrow and blood of treated patients.

According to a National Cancer Institute (NCI) statement, Gleevec represents a new way of thinking about cancer. The molecularly targeted drugs are different because they go after abnormal proteins needed by the cancer itself.

Most current cancer therapies kill both cancer and normal cells. Gleevec zeroes in on specific cancer-causing molecules and spares healthy cells.

"The drug targets only abnormal cells, and corrects the problem that causes cancerous cells to grow out of control," said Ralph Vogler, MD, scientific program director for extramural grants for the American Cancer Society (ACS). "This is another example of the emerging importance of this new class of drugs, the molecular target drugs."

According to news reports, in a study published in Science a few months after the FDA approval, Charles Sawyers, MD, a cancer specialist at Jonsson Cancer Center at the University of California, Los Angeles, said two factors have caused some patients with very advanced leukemia to develop resistance to Gleevec.

Sawyers said the problem lies in a genetic mutation and the excessive production of an enzyme. As the leukemia advances, the cells produce more of the enzyme which Gleevec targets. This increased production overwhelms Gleevec’s ability to control cell growth. Sawyers and his group studied 11 patients in the blast crisis phase who initially had responded to Gleevec and then relapsed.

Experts warn that Gleevec is no magic bullet, but that it holds much promise not only for CML, but for other cancers. According to a recent Scientific American article, Larry Norton, MD, at Memorial Sloan-Kettering Cancer Center in New York City, said Gleevec is a milestone because of its revolutionary strategy in treating cancers on the molecular level.

The FDA used an "accelerated approval" of Gleevec to make the drug available to patients right away after scientists, including Brian J. Druker, MD, of Oregon Health Sciences University, discovered its success. The approval was based on three studies that included 1,000 patients.

After the approval, US Health and Human Services Secretary Tommy Thompson said, "It's important to realize that although the approval was fast, it is the culmination of years of work."

The researchers found that side effects were generally less severe than with more conventional cancer treatments, though some patients reported a degree of nausea and vomiting.

"One of the most amazing things about [Gleevec] to me has been its lack of side effects, and most patients are telling me that they've felt better than they have in many, many years," Druker said in an interview during early study of the drug.

Gleevec was approved under the FDA's orphan drug program set up to provide financial incentives for drug development to treat rare diseases. Approximately 4,700 new cases of CML were expected in the US in 2001, with about 2,300 deaths. Further studies are underway to improve the effectiveness of Gleevec, either as a single drug or in combination with other drugs which work on the same diseases, such as interferon in CML.