A test that checks for activity by a gene mutated in the most common form of lung cancer can help predict which patients will be helped by AstraZeneca’s targeted drug Iressa, U.S. researchers reported on Tuesday.

The finding, published in the Journal of the National Cancer Institute, could help doctors pick out patients who should be treated with Iressa, which has remarkable effects in a small percentage of patients.

Non-small cell lung cancer accounts for about 85 percent of all cases of lung cancer, which killed more than 157,000 men and women in the United States last year. It is by far the leading cancer killer globally and is very difficult to cure.

Just 15 percent of patients survive more than five years.

Iressa was the first drug to work well against lung cancer, but it helps fewer than 15 percent of patients.

In non-small cell lung cancer, the epidermal growth factor receptor (EGFR) gene is mutated and the cells proliferate out of control to form a deadly tumor. Iressa, known generically as gefitinib, targets EGFR.

Last year researchers identified a specific mutation in EGFR that predicted who would be helped by Iressa. But it is not a precise test, as some people without the mutation were helped by the drug and some people with the mutation developed resistance.

Dr. Fred Hirsch of the University of Colorado Cancer Center and colleagues looked for an easier and better test. They used one made by Abbott Laboratories Inc. that uses a technology called fluorescence in situ hybridization or FISH to find out how many copies of the gene each patient had.

They found that patients whose tumor cells carried extra copies of the EGFR gene responded better to Iressa.

Writing in the Journal of the National Cancer Institute, they said they studied 102 lung cancer patients with advanced disease.

They found 33 of the 102 patients had several copies of EGFR, and 36 percent of them were helped when treated with Iressa. Just 3 percent of the patients who did not have extra EGFR responded to the drug.

These 33 patients also lived longer - nearly 19 months compared to seven months.

This makes the Abbott assay “an ideal test for selecting candidate NSCLC (non-small cell lung cancer) patients for gefitinib therapy”, they wrote.

Hirsch’s team also found that some patients with stable disease had no EGFR mutations and said this needed further investigation.

Other targeted drugs for EGFR include OSI Pharmaceuticals Inc.‘s, Roche Holding AG’s and Genentech Inc.‘s Tarceva. Other companies are also developing EGFR blockers, including Abgenix Inc., working with Amgen Inc.