The US Food and Drug Administration on Monday approved a new drug, Iressa (gefitinib), for the treatment of advanced non-small cell lung cancer. The drug is approved for use only in patients whose tumors have progressed after standard chemotherapy treatment with platinum-based drugs and docetaxel.

“FDA believes it is crucial for cancer patients to have many safe and effective treatment options available to them,” agency commissioner Mark McClellan, MD, PhD, said in a statement. “With the approval of Iressa, thousands of patients with lung cancer will now have access to an additional treatment after others haven’t worked to stop the progression of their disease.”

Lung cancer is the leading cause of cancer death among both men and women in the United States. The American Cancer Society estimates that 171,900 people will get lung cancer this year, while 157,200 will die from it. Non-small cell lung cancer accounts for about 80% of lung cancer cases.

Iressa was approved as part of the FDA’s accelerated drug approval program, which is intended to give patients with life-threatening diseases earlier access to promising treatments. Under the program, a drug may be approved before all the clinical trials usually required for approval have been completed. Iressa’s manufacturer, AstraZeneca, is required to conduct additional clinical trials to prove the how well the drug helps patients.

“Studies are needed to confirm the clinical benefit, understand better which patients benefit, and evaluate long-term safety,” McClellan said.

Safety and efficacy have been areas of concern with this drug.

Some earlier clinical trials found that Iressa did not increase survival or reduce symptoms of the disease when used in combination with chemotherapy. (The FDA did not approve the drug for this use.)

And in Japan, where Iressa was approved for use last year, a small percentage of patients experienced a serious side effect called interstitial lung disease (ILD), a condition that causes inflammation, scarring, and tissue damage in the lungs. In some cases, the patients died from the ILD.

For these reasons, the consumer advocacy group Public Citizen urged the FDA not to approve Iressa. “The FDA would be putting patients in jeopardy by approving a drug that is already showing itself to be ineffective and dangerous,” Sidney Wolf, MD, director of Public Citizen’s health research group, said in a statement. “The severity of adverse events… should be a red alert to the agency.”

But the FDA said the benefits of Iressa outweighed the risks of side effects.

The agency said it extended its review of the drug by three months to consider these reports. The FDA looked at data from approximately 23,000 patients who have taken the drug and determined that about 2% of Japanese patients had developed ILD, while just 0.3% of US patients had developed it. About one-third of patients who got ILD died from it, the FDA said.

On the other hand, patients with advanced non-small cell lung cancer often have few treatment options available to them, and once standard chemotherapy drugs stop working, life expectancy is often short.

In approving the drug, the FDA considered the results of a clinical trial involving 216 patients, of whom 142 had tumors that were no longer responding to prior treatments. About 10% of patients given Iressa responded to the treatment, meaning their tumors shrank by at least 50% and stayed smaller for at least a month. The average duration of response was seven months. Women seemed to have a better response than men; non-smokers also did better on the drug than smokers.

Additional studies will be conducted to determine whether Iressa prolongs survival and decreases cancer symptoms in patients with tumors that are resistant to other therapies.

Iressa is one of a new class of targeted cancer therapies, which attack cancer cells while leaving most normal cells unharmed. Iressa targets a protein receptor on cancer cells called epidermal growth factor receptor (EGFR), which causes the cancer cells to divide rapidly. By stopping this rapid cell division, Iressa may help slow cancer growth.

The drug is taken once a day as a 250 milligram pill, according to the manufacturer. Possible side effects include diarrhea, nausea, vomiting, rash, and acne. The drug can harm a developing fetus, and so should not be taken by pregnant women. It can also increase bleeding in patients taking the blood thinner warfarin.