By now, it's a given that smoking causes lung cancer. The American Lung Association reports that 80 to 90 percent of all cases of lung cancer are smoking-related.

The remaining 10 to 20 percent, though, has been more of a mystery — until now. A new line of research has implicated thye sexually transmitted infection human papillomavirus, or HPV, in lung cancers that were found in non-smokers.

HPV is the leading cause of all cervical cancer cases in the world. It's a well-known disease that's gottena lot of press in recent years; an effective vaccine was recently developed that can prevent the viral infection and subsequent cervical cancer development. Whether or not the vaccine should be required for teenage girls has become a hot-button political issue.

Adding fuel to the fire, a research team from the Fox Chase Cancer Center recently looked at tissue samples from lung cancer patients who had no history of smoking and saw that close to 6 percent showed evidence that they had been driven by HPV infection.

Four out of 36 lung samples had signs of infection from two strains of HPV known to cause cancer. Looking more closely at the two samples infected by one strain of HPV, Dr. Ranee Mehra, MD, attending physician in medical oncology at Fox Chase and her team saw signs the virus had integrated into the tumor's DNA — which is even more suggestive that the infection had caused the tumor in the first place.

Dr. Mehra noted that non-smoking related lung cancers kill 100,000 people a year, so 6 percent of those cases having a known and preventable cause could save lives.

It is not known how the virus could travel down to the lungs. However, Dr. Mehra notes that there is highly convincing data indicating that HPV had directly caused the tumors rather than the person just having cancer and an unrelated HPV infection. "The presence of both simultaneously, and the integration of the virus into the tumor's DNA, fuels the hypothesis that they are related," stated Dr. Mehra.

HPV is widely known to cause a range of cancers, including cervixal, throat, head, and neck cancer. The virus has also been implicated in a drastic rise in the number of throat and oral cancers related to oral sex. There was no comment from the research article indicating that oral sex may be associated with the risk of HPV related lung cancer.

Mount Sinai Hospital, in New York City, has an interesting infographic that explains the risk of cancer from oral sex.

The current research was presened at the American Association for Cancer Research Annual Meeting 2013 on Wednesday, April 10.