Although smoking is the No. 1 cause of lung cancer, viruses may also contribute to the development of this fatal disease, new research suggests.

Dr. Arash Rezazadeh and colleagues from the University of Louisville, Kentucky presented their findings at the 1st European Lung Cancer Conference, jointly organized by the European Society for Medical Oncology (ESMO) and the International Association for the Study of Lung Cancer (IASLC) in Geneva.

For the study, the researchers examined lung cancer tissue samples taken from 23 patients, all smokers. Six samples tested positive for HPV, although one case resulted from cervical cancer that spread to the lungs. The remaining five HPV-positive samples comprised the following stains: HPV-16, HPV-11, and HPV-22.

“The fact that five out of 22 non-small-cell lung cancer samples were HPV-positive supports the assumption that HPV contributes to the development of non-small-cell lung cancer (NSCLC),” the study authors say in a news release, Webmd.com reports.

“We think HPV has a role as a co-carcinogen which increases the risk of cancer in a smoking population,” Dr. Rezazade said.

He added that more study needs to be done in the near future. “In terms of HPV, our finding is pretty controversial. And this is just the beginning of the road. There is much more work to be done. But it's important to know that being infected with this virus does appear to increase lung cancer risk.”

However controversial or not the findings of the study are, they raise an intriguing question: Could an HPV vaccine similar to Gardasil, the one approved to protect women against cervical cancer, also help thwart lung cancers?

According to the American Cancer Society, more than 161,000 in the U.S. will die from lung cancer in 2008.

Another study by Israeli researchers, presented at the same conference, found a connection between a virus and non-small-cell lung cancer. In a study on 65 lung cancer patients, of whom 90 per cent were smokers, they found that the measles virus was present in 54 per cent of the lung samples tested.

“Measles virus is a ubiquitous human virus that may be involved in the pathogenesis of lung cancer. Most likely, it acts in modifying the effect of other carcinogens and not as a causative factor by itself,” said lead author Samuel Ariad from Soroka Medical Centre in Beersheba, Israel.