A Philadelphia medical centre the Fox Chase Cancer Centre is offering a high-tech DNA test which can identify the genetic mutations driving an individual patient’s cancer.

Other leading medical centres and biotech firms are launching similar tests, which should help doctors make cancer care more effective and less harmful to the patient.

Leading 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 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.”

“But the more patients tested the more we understand what factors is driving cancer”.

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 very severe.

Newer targeted drugs, in contrast, selectively interfere with a genetic chain reaction, or “pathway,” that malignant cells use to survive and grow.

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.

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 random 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.

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.

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.