Narrator: This is Science Today. It's estimated that there are at least six or seven mutations involved in the development of lung cancer. John Wiencke, a professor of epidemiology at the University of California, San Francisco, says a mutation known as K-ras, which is found in about 10 percent of all lung cancers, may be the first to occur in the disease pathway.

Wiencke: So, it could be that a person starts smoking, develops a K-ras mutation and then not there could be, I think, decades - you know, literally tens of years between the induction of the mutation and the actual cancer.

Narrator: Wiencke says this is actually good news.

Sessler: We may have time to intervene and block this effect before cancer actually occurs. This particular test that we ran to identify K-ras mutations isn't even used right now in the clinic. It may be if our findings are confirmed they may decide that it's useful to actually run this test routinely on patients.

Narrator: For Science Today, I'm Larissa Branin.