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In CML, the aberrant protein signals blood cells -- white blood cells in particular -- to proliferate at a rapid rate and not die. If left unchecked, those cells will eventually clog the body, turning blood into something that looks more like pus. Gleevec stops the abnormal protein from working and stops the proliferation signal from getting through. The cancerous cells stop reproducing and die.
Mr. Miller heard about the drug while it was still being tested. He applied to be part of a clinical trial in Portland, Ore.
The conventional treatment for CML -- a drug called interferon -- had almost killed him in 1999. It was supposed to boost his immune system to fight cancer. Instead, it gave him congestive heart failure.
It was a complete disaster," Mr. Miller says. "I couldn't breath. I was in a fog. I didn't even know who I was. In the photographs from the time, I look like a dead person." In March, 2001, he flew to the United States and started the new, targeted drug. He immediately started to feel better. "It was magical," he says.
Two months later, Gleevec was approved by the U.S. Food and Drug Administration. By the fall, Health Canada had followed suit. Today, Gleevec is the first line of treatment for patients in the early stages of the disease.
A five year follow-up study, presented in June, found that of 553 patients who started on the drug, 69 per cent were still taking it. Ninety-three per cent of them have survived without their cancer progressing to a more aggressive stage, and 87 per cent have no sign of cancerous cells in their blood.
But there are downsides.
Gleevec is not a cure; patients may have to stay on it for the rest of their lives. Many who take it suffer side effects, some so serious they have to get off the drug. It may cause heart problems in a small number of patients. Those in the later stages of CML frequently develop resistance, and the drug stops working.
It is effective only against two rare cancers: CML and a type of gastrointestinal tumour. Still, Gleevec is widely regarded as a phenomenal success story in a field where breakthrough drugs add mere months or weeks to patients' lives.
The big question is whether that success can be repeated with more common forms of the disease, such as breast, colon or prostate cancer. There are signs it won't be easy.
Gleevec wasn't the first targeted cancer drug. There have been a number of them, including Herceptin, which in some women helps prevent breast cancer from returning. But most targeted drugs, including Herceptin, have worked only in combination with conventional chemotherapy drugs. None have been as effective as Gleevec.
Why? There are roughly 200 kinds of cancer, and CML may be one of the rare versions of the disease with such a clear target.
This fall, researchers at Johns Hopkins University in Baltimore set out to map all the genetic changes involved in colon and breast cancer. They expected to find a handful of genes that help tumours grow. They found nearly 200. Most tumours averaged 11 of them.
This makes it hard to imagine that a drug like Gleevec, designed to target a single protein, will work for breast, prostate or colon cancer, says Vincent Giguère, a researcher at the McGill University Health Centre in Montreal.
However, a combination of them might do the trick.
"Think of a cocktail of drugs like the ones now used to treat HIV-AIDS," Dr. Giguère says. "That is how we are going to outfox cancer cells."
Researchers are working to identify all the mutations involved in different forms of cancer. Once that's finished, they will have to figure out the abnormal proteins they make and come up with drugs to block them.
By then, doctors should be able to do a genetic profile of every tumour -- identifying the mutations -- so they can concoct the most potent drug cocktail possible for each patient, Dr. Giguère says. The combination of targeted drugs and personalized medicine could transform cancer from a killer disease into a chronic one.
"This will take 20 or 30 years," Dr. Giguère says. "I think I will see it in my lifetime, and I am 50."
It may be possible to zero in on the most dangerous cancer cells.
Cancer doesn't become deadly until it spreads, or metastasizes, and many cancers follow a particular pattern.
Breast-cancer cells, for example, often move to the bones. This is quite a feat, since they first have to morph from breast cells into bone cells, Dr. Giguère says. He and his colleagues are trying to figure out how they do it -- what makes them different from the cells in the bulk of the tumour, which stay in the breast?