DNA test analyzes genes known to contribute to cancer
PHILADELPHIA - Embracing the promise of personalized medicine, Fox Chase Cancer Center is offering a high-tech DNA test that can identify the genetic mutations driving an individual patient's cancer.
Other leading medical centers and biotech firms are launching similar tests, which should help doctors make cancer care more effective and less toxic.
Experts say this customized approach will become increasingly important as the arsenal of drugs that target cancer genes grows.
For patients at the forefront, however, the value of cutting-edge DNA testing is hard to predict. The list of defects that drive cancer is growing much faster than the ability to curb them. The Fox Chase test, CancerCode-45, analyzes 45 genes known to contribute to the development of cancer, but not all are treatable or even fully understood.
Also, Fox Chase is offering the $3,000 test only to patients with advanced cancer who have exhausted standard treatment options.
"The reality that patients must be aware of is that this technology will not benefit everyone," said Jeff Boyd, executive director of Fox Chase's Cancer Genome Institute.
He said at least a third of tested patients would get information they could act on, but conceded, "We don't know what fraction it will benefit."
Along with surgery and radiation, cancer treatment has long relied on chemotherapy -- drugs that indiscriminately poison fast-growing cells, both healthy and malignant. But chemotherapy doesn't work, or works only temporarily, in most patients, and the side effects can be severe.
Newer targeted drugs, in contrast, selectively interfere with a genetic chain reaction, or "pathway," that malignant cells use to survive and grow. Avastin, for example, turns off VEGF, a key protein in the growth of new blood vessels that feed tumors. Herceptin blocks a growth factor, her2, that is overproduced in some aggressive breast cancers.
The advent of targeted therapies marks a change in our understanding of cancer, experts say. Rather than a disease of a particular organ, cancer is a cumulative process of genetic changes that can arise in various organs. That's why Avastin works in some cancers of the lung, kidneys, and brain, while Herceptin is effective against some gastric (stomach) cancers as well as breast tumors.
Recent studies, Boyd said, show that some head and neck cancers might also be fueled by her2 overproduction, so "Herceptin might help."
Until now, figuring out whether a targeted therapy could help meant testing a patient's tumor sample for that drug's target. But with dozens of targeted drugs on the market, and counting, this piecemeal approach has become problematic.
DNA sequencing technology, meanwhile, has undergone a revolution in recent years. Scientists can sequence a patient's genetic code -- all three billion chemical pairs of DNA -- rapidly and affordably.
By homing in on genes implicated in cancer, CancerCode and similar tests can keep costs, turnaround time -- and sequencing errors -- to a minimum. CancerCode provides results in 16 days.
Stuart M. Brown, a New York University cell biologist and bioinformatics expert who was not involved in developing CancerCode, said that "the Fox Chase test is looking at the 45 biggest 'red flag' genes, so they have greatly simplified some of the problems of the technology. They can study those genes more carefully, and accumulate knowledge about every letter in those genes."
Such DNA tests might reduce medical costs by sparing patients months of treatment with drugs they don't respond to. That would make testing attractive to health plans.
But CancerCode is not yet covered by insurance, and patients are warned that test results may warrant using a therapy that would not be covered.
For Fox Chase, the test will not be a money-maker, Boyd said. The DNA analysis costs more to do than patients will be charged, and the test will be expanded as more cancer genes are discovered. Fox Chase is also planning studies in which patients would pay nothing for the test.
"We feel a moral obligation to be in that innovator role," Boyd said. "This is a test that will be under constant evolution."
Contact Marie McCullough at 215-854-2720 or [email protected] ___
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