ORLANDO -- Researchers reported new gains in both treatment and prevention of lung cancer at the 38th annual meeting of the American Society of Clinical Oncologists (ASCO), in Orlando, Fla.

In an example of the growing success of the new "molecular target" drugs, an oral cancer drug similar to the new leukemia drug Gleevec has for the first time shown such drugs can work against non-small cell lung cancer (NSCLC). These drugs attack targets present or abundant only on cancer cells leaving normal cells largely unharmed.

Mark Kris, MD of Memorial Sloan-Kettering Cancer Center in New York City and his colleagues treated 216 patients whose NSCLC had spread within the lung or to other parts of the body, and in whom chemotherapy was no longer working or had too many side effects.

In those taking the drug gefitnib, also called Iressa, lung tumors shrank by half or more in 12% of the patients, and in 43%, symptoms such as shortness of breath, cough, weight loss, and mental clarity improved, usually by the second week of treatment.

"Iressa gives us a whole new way to fight lung cancer and raises our hopes that this disease can be attacked even more effectively by blocking other cellular growth signals," said Kris.

The drug is a once-a-day pill, and most of the side effects were limited to mild diarrhea and a skin rash.

The trial is the first success against lung cancer for one of the new class of "molecular target" drugs.

Although Iressa, manufactured by Astra Zeneca, has a different target than Gleevec — Iressa focuses on a growth-promoting protein called epidermal growth factor receptor (EGFr) — both drugs work by blocking the pathway of chemical signals within cancer cells that tell them to grow and divide.

The drug can be taken for long periods of time, and patients in the now-closed trial took the drug for an average of 18 months, with one patient on it for about three years.

In the future, it may be possible to tell from patients' tumor samples who is most likely to respond to the drug, allowing doctors to better tailor therapies to their patients, said study co-author Karen Kelly, MD, of the University of Colorado Health Sciences Center in Denver.

The chief medical officer of the American Cancer Society (ACS) says the first-time success of a molecular target drug against lung cancer points to the increasing value of such drugs in the fight against cancer.

"We know Iressa has activity against other cancers as well, including breast cancer, colon cancer, and others, and is a relatively non-toxic drug," said Harmon Eyre, MD, vice-president for medical affairs and research at the ACS.

"Now it will likely get more widespread testing, and hopefully that will be the next step in making these better drugs available for a variety of different cancers," said Eyre.

In another study presented at ASCO 2002, researchers reported that a substance that helps restore lung cells' ability to absorb vitamin A may have the potential to help prevent lung cancer in former smokers, but they caution that more study is necessary.

"We've shown in this study that 9-cis retinoic acid is biologically active in the lung," said the study's lead author, Jonathon A. Kurie, MD, of the M.D. Anderson Cancer Center in Houston.

On their surfaces, lung cells have proteins called retinoic acid receptors (RARs) that absorb vitamin A, which is known to protect against lung cancer.

But heavy smoking cuts the number of RARs, said Kurie.

So Kurie and colleagues studied 226 former smokers who had smoked at least the equivalent of a pack a day for 20 years, to see if a form of vitamin A could help cells regain more of the receptors.

Daily for three months, some of the former smokers got 9-cis retinoic acid, some got another form of retinoic acid plus vitamin E, and others got a pill with no active ingredients.

Receptors increased significantly only in those taking 9-cis-retinoic acid.

"These results now deserve further study in a larger group of patients," said lead author Kurie.

That doesn't mean it's safe to take large amounts of vitamin A, or similar substances, Kurie noted.

Vitamin A in large amounts is toxic, and taking large amounts of beta-carotene, another vitamin A-like substance, proved to raise lung cancer risk in former smokers, he added.

The best defense against lung cancer is not to smoke, but half of all new lung cancer cases in the US are in former smokers, so work to help prevent cancer in those at such high risk must continue, said Kurie.