''When they presented with the cancer, those [patients] who took one of these drugs were much less likely to have metastatic disease," says researcher Peter J. Mazzone, MD, MPH, lung cancer program director of the Respiratory Institute at the Cleveland Clinic in Ohio.
He is presenting his findings this week at CHEST 2010, the annual meeting of the American College of Chest Physicians, in Vancouver, British Columbia, Canada.
The new findings echo those of other recent research, Mazzone tells WebMD, including an animal study done by National Cancer Institute researchers and other research linking metformin with lower cancer rates in general.
Metformin and TZDs for Lung Cancer
For the new study, Mazzone and his colleagues are evaluating the records of more than 600 people with diabetes and lung cancer, he tells WebMD. He reported on 225 of the 600 at the CHEST 2010 meeting.
''We matched them to diabetics who did not have lung cancer," Mazzone tells WebMD.
Overall, people on the drugs were less likely to get lung cancer, and people with lung cancer were less likely to have it spread and to have longer survival if they were on one of the diabetes drugs before their diagnosis.
"When they presented with the cancer, those who took one of the drugs were much less likely to have metastatic disease," Mazzone says.
In people on metformin alone, TZD alone, or both, 25% of the lung cancer patients had metastases, while 48% of those on neither drug did, Mazzone tells WebMD.
"People who take the drugs seem to develop lung cancer less often," Mazzone says. "Ninety-six percent of people who didn't get cancer were taking one of the drugs and 41% of those who did get cancer were."
The drugs may also lengthen survival, Mazzone found.
Why the diabetes drugs seem to make lung cancers less likely and, when it occurs, less likely to spread, isn't known for sure, Mazzone says.
"There are several pathways these drugs work through that are [also] known to slow the growth of cancer cells, and to affect the pathways known to lead to cancer growth," Mazzone says.
Several other studies, many of them with many more patients than the new study, have also concluded that the diabetes drugs slow lung cancer progression, says Kemp Kernstine, MD, PhD, a lung cancer specialist and director of the lung cancer and thoracic oncology program at the City of Hope Comprehensive Cancer Center, Duarte, Calif., who reviewed the findings for WebMD.
In other research, metformin has been shown to activate an enzyme, called AMP-activated protein kinase, known to inhibit another protein, mTOR, which regulates cell growth and survival in lung tumors induced by tobacco carcinogens, Kernstine says.
''There are companies working on this pathway," he says, developing drugs to target it. Eventually, he says, doctors may be able to identify patients at high risk for lung cancer -- such as those with exposure to asbestos -- and put them on these drugs.
But more research is needed, he says, noting the small size of the Cleveland Clinic study. "You really need to look at a larger population."
It's premature, he says, to go on metformin for lung cancer risk reduction. "I would not rush out to tell your doctor to put you on metformin, even if you are a type 2 diabetic," he says. Like all medicine, metformin can have side effects, he says.