Oct. 22 (Bloomberg) -- Lung cancer's growth and lethal spread may be tied to more than two dozen mutated genes, according to a study that may help doctors identify effective drugs.

About two-thirds of the altered genes hadn't been associated with lung cancer until now, and half of them had never been associated with any cancer, said Matthew Meyerson, a member of the international team that conducted the work. The study was released today by the journal Nature.

Lung cancer grows quickly and is difficult to treat, leaving about 85 percent of patients dead within five years of diagnosis. Most lung cancers are linked to smoking tobacco, yet most smokers don't develop the disease. Understanding what the genes do and how they malfunction may help speed the development of new drugs for lung tumors, which kill more than 1 million people annually worldwide, said Meyerson, a Harvard Medical School pathologist.

``We're seeing more evidence that treatments directed against mutated gene products and proteins are effective for cancer,'' he said yesterday in a telephone interview from his office in Boston.

The findings may help explain the role of cigarettes, which are linked to about 90 percent of lung cancers. The study found smokers' tumors each had an average of about 49 gene mutations, compared with an average of five in the tumors of never-smokers. Studies of other tumor types have linked high levels of gene mutation to faster cancer spread and greater ability to overcome treatments, the researchers said.

Gene Mutations Key

Genes contain the instructions for making proteins, the building blocks of all cells and tissues. Mutations in certain genes, often those that control cell division and growth, can lead cancers to form and spread throughout the body, researchers said.

Traditional cancer treatments kill rapidly growing cells, and work best early in the disease. Lung cancers often avoid early detection before they've spread widely, and often resist available drugs.

To get a clear of idea of what makes lung cancers grow, a team of scientists from about 19 labs and institutions in the U.S. and Germany analyzed the genes of 188 lung tumors taken from patients.

The researchers looked at 600 genes from each tumor and copied the genes' sequences -- the code of chemical base components represented by the abbreviations A, C, G and T -- and compared them to versions of the same genes from normal non- cancerous tissue.

Finding Cancer's Roots

The study is ``a strong beginning to untangling the roots of this disease, which has proven to be so challenging,'' said Bradley Ozenberger, a scientist at the U.S. National Human Genome Research Institute in Bethesda, who helped write the study. Three of the genes with mutations linked to lung cancer normally make proteins that suppress the formation of tumors, Meyerson said. While mutations in these genes had been linked to other cancer types, they hadn't been associated with lung cancer before, he said.

Another gene the study linked to lung cancer for the first time, called EPHA3, is in the family that makes tyrosine kinases, which many organisms use during growth and development. AstraZeneca Plc's Iressa blocks a tyrosine kinase called epidermal growth factor receptor, and is undergoing tests against lung cancer, Meyerson said.

The study was led by Li Ding of the Genome Sequencing Center at Washington University in St. Louis, and was funded by the National Human Genome Research Institute.

To contact the reporter on this story: John Lauerman in Boston at jlauerman@bloomberg.net.

Last Updated: October 22, 2008 15:33 EDT