The US Food and Drug Administration (FDA) is taking another look at the lung cancer drug Iressa (gefitinib) because a large clinical trial showed it does not help most patients live longer.

The drug's maker, AstraZeneca, informed the FDA of the study results late last week. The study involved nearly 1,700 patients with advanced non-small cell lung cancer that had not responded to other treatments, including chemotherapy.

Patients who took Iressa lived about 5.6 months, while those given a placebo lived about 5.1 months; the difference was not statistically significant.

Because of this result, AstraZeneca sent a letter to doctors urging them to consider other treatments before putting new patients on Iressa. The drugs Taxotere (docetaxel) and Tarceva (erlotinib) have both been shown to help lung cancer patients live longer.

Tarceva, which was approved for advanced lung cancer just last month, is a very similar drug to Iressa. Both are EGFR (epidermal growth factor receptor) inhibitors; they block a signaling pathway that cancer cells need to grow.

Most doctors familiar with both drugs believe there are few differences between them, said Jennifer Temel, MD, a medical oncologist at Massachusetts General Hospital in Boston who treats lung cancer patients.

The study results that showed Iressa didn't help may have been due to chance, she said. But they may still make a difference in which drug doctors choose first.

"I think if we have a new patient who we're going to start on EGFR therapy, we'll start them on Tarceva," she said. "If we have someone who is not responding to Iressa, we'll try Tarceva. But if we have someone on Iressa who's doing well, we'll continue with Iressa."

AstraZeneca said it will continue to make Iressa available to patients who are using it with good results.

The FDA said patients already on Iressa should talk with their doctor about whether to keep taking the drug. The agency is looking at the results of recent studies to determine whether it should pull Iressa off the market or take some other action.

Iressa was approved in 2003 under the FDA's accelerated approval program, which makes promising drugs available to the public if there's a good chance they will help patients. The drug was approved as a last resort for people who weren't helped by other treatments because it did shrink lung tumors in about 10% of the people who took it. But, the FDA also required Astra-Zeneca to conduct this larger trial to see if it would prolong the life of people with advanced lung cancer.

Earlier this year, research teams in Boston discovered some genetic mutations that seem to make people more responsive to the drug. All the cancers were a type called adenocarcinoma or bronchoalveolar carcinoma. About 40% of all lung cancers are these types. A test is now available to look for those mutations.