Viruses too could contribute to the development of lung cancer, US researchers say.
Although smoking is the No. 1 cause of lung cancer, viruses may also play a part, say scientists from the University of Louisville, Kentucky.
Actually they seem to believe that the virus-infected cells turn cancerous only because of exposure to cigarette smoke.
They presented their findings Friday at the 1st European Lung Cancer Conference in Geneva.
In a study of 23 non-small-cell lung cancer samples, researchers found six that tested positive for the human papilloma virus, or HPV. HPV, a highly prevalent pathogen that is often sexually transmitted, is the virus responsible for many cases of cervical cancer.
Two of the samples tested positive for HPV type 16, two were HPV type 11 and one was HPV type 22. In one case, it was found that cervical cancer had spread to the lungs through metastasis.
"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," the authors say.
Because all of the participants in the study were smokers, the presence of HPV was seen to play a part in the development of the cancer. They theorize that the lung tissue cells infected with HPV may have a higher risk of becoming cancerous when exposed to cigarette smoke, reports CBC News, Canada.
"We think HPV has a role as a co-carcinogen which increases the risk of cancer in a smoking population," said Arash Rezazadeh, lead author of the study, in a release.
The authors say the discovery has "significant implication" considering the recent introduction of HPV vaccinations in school-age girls to prevent cervical cancer.
Another study presented at the conference by Israeli researchers also 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," said lead author Samuel Ariad from Soroka Medical Centre in Beersheba, Israel. "Most likely, it acts in modifying the effect of other carcinogens and not as a causative factor by itself."