Some doctors are changing the way they treat lung cancer, the most lethal type of cancer for both men and women, after new studies added to the concept of giving certain drugs continuously to battle the disease in hopes of prolonging lives without the side-effects of initial treatment with chemotherapy.

Most patients with advanced non-small cell lung cancer are treated with four-to-six rounds of chemotherapy drugs in order to slow tumor growth. Chemotherapy kills cancer cells but also affects healthy cells and can cause significant side effects including nausea, vomiting and fatigue.

Many doctors also give drugs like Avastin or Tarceva in addition to chemotherapy. Avastin, marketed in the U.S. by Roche Holding AG's (RHHBY) Genentech unit, blocks blood vessels that feed cancerous tumors while Tarceva, also marketed by Genentech along with OSI Pharmaceuticals Inc. (OSIP), blocks an enzyme involved in cancer growth.

However, once chemotherapy ends, doctors typically stop all treatment until the cancer starts growing again or progresses because giving continuous chemotherapy makes patients sicker from side effects.

But new studies have suggested that maintaining treatment with targeted agents like Avastin and Tarceva as well as Alimta, a chemotherapy drug from Eli Lilly & Co. (LLY) that doctors say is far less toxic than traditional chemotherapy, could be a new approach to treating cancer.

Two of the most recent studies were released over the weekend at the American Society of Clinical Oncology's annual meeting. One showed patients receiving Alimta after being treated with other chemotherapy drugs lived for about three months longer than patients not receiving the drug. The other study showed that adding Tarceva to treatment with Avastin after patients had been previously treated with other drugs slowed average cancer growth by an additional month.

"We don't cure patients," said Roman Perez-Solar, the chairman of Montefiore-Einstein Cancer Center in New York City. But, he said doctors no longer have to wait until patients relapse or have their cancer get worse until they start new treatments.

Most people with lung cancer are diagnosed with advanced stage disease that cannot be surgically removed or has spread to other parts of the body. The majority of people with advanced lung cancer survive less than one year.

Perez-Solar said he currently has just a few patients on continuous maintenance therapy, but said the new studies provide additional evidence to treat more patients continuously.

"It's definitely an option to discuss with patients," he said.

OSI Pharmaceuticals and Genentech have filed an application with the Food and Drug Administration seeking approval to market Tarceva as a maintenance therapy.

Gabriel Leung, OSI's president of oncology, said until recently there were few drugs approved to treat lung cancer so doctors waited until the disease worsened before adding treatments, partly because of the side-effects of chemotherapy, but also so they didn't want to quickly exhaust the supply of available drugs.

"Now with more and more therapy there's not a lot of reason to wait anymore," he said.

Bruce Johnson, the director of the Dana-Farber Harvard Medical Center Lung Cancer program, noted that lung-cancer is one of the most difficult types of cancer to treat. Most patients are diagnosed with advanced stages of the disease when tumors usually can't be successfully removed by surgery.

He said those patients later get additional treatment once their tumors start growing again. The ultimate goal of therapy is to stop or slow the growth of lung cancer for several years, but without the significant side effects of chemotherapy.

Johnson, who is involved in research of an AstraZeneca PLC (AZN) compound Zactima, which essentially combines the mechanism of Avastin and Tarceva into one pill, said he's had lung-cancer patients on Zactima for years. AstraZeneca has said it plans to soon file for FDA approval of Zactima.

-By Jennifer Corbett Dooren, Dow Jones Newswires; 202-862-9294; jennifer.corbett@dowjones.com