A newly published study links the sexually transmitted human papillomavirus, or HPV, to lung cancer, adding lungs to the list of organs scientists say are susceptible to cancer as a result of contracting the most common sexually transmitted infection in the United States.
Recent studies have found connections between HPV and cancers of the mouth and throat, but the University of Louisville study released late last week is the first to associate the infection with lung cancer.
HPV has long been known to result in cancers of the sex organs, particularly the cervix, and a vaccine targeting young women and girls was introduced in the United States in 2006.
Conservative parents and activists have condemned the vaccine, marketed under the name Gardasil, since it was approved by the Food and Drug Administration last year, claiming it would -- like easily available condoms -- encourage young people to engage in promiscuous sex.
Those same parents and groups say the news showing a link between the virus and lung cancer, which means it could affect not only their daughters but also their sons, does not change their opposition to the drug.
At a conference this week in Geneva, Dr. Arash Rezazadeh from the University of Louisville presented the findings of the study, which found HPV in six out of 23 lung cancer samples.
"The researchers found six samples that tested positive for the presence of human papillomavirus, the virus that also causes many cases of cervical cancer. One was later shown to be a cervical cancer that had spread to the lungs," read a statement from the First European Lung Cancer Conference.
All the samples came from smokers, and authors of the study said smoking remains the most important factor in the development of lung cancer. But "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," they said.
"We think HPV has a role as a co-carcinogen which increases the risk of cancer in a smoking population," Rezazadeh said in a statement.
Rezazadeh was in Switzerland for the conference and unavailable for comment.
According to the Centers for Diseases Control and Prevention, some 20 million Americans are infected with HPV, and another 6.2 million become newly infected every year. Some strains of the disease result in genital warts, but other strains can, over time, develop into cancer.
The American Cancer Society estimates that in 2008, 11,070 women will be diagnosed with cervical cancer in the United States.
Other HPV-related cancers include vulva, vaginal, penile and anal.
Though the study is the first to note the combined effects of smoking and HPV on the lungs, doctors have known for a while that women who smoke and contract HPV are more likely to develop cervical cancer than nonsmokers, said Dr. Lauren F. Streicher, an OB/GYN and professor at Northwestern Medical School.
"Smoking plays a key role in the rate of conversion to malignancy in cervical cancer too," she said. "Seventy to 80 percent of women are exposed to HPV, but less than 1 percent of women get cervical cancer. We know lesions on the cervix are more likely to become cancerous in smokers."
HPV is generally contracted through the skin during sex. With the exception of the one lung cancer sample that originated with cervical cancer, the mechanism by which the lungs became infected was not clear from the study.
Though the Louisville study does not discuss the efficacy of the HPV vaccine in treating lung cancer, the vaccine targets the same cancer-causing type of the virus found in the lung cancer samples -- type 16.
"Type 16 is the one that causes cancer," Streicher said. "As more of these studies are completed, we're learning that the vaccine would clearly be preventive in many different kinds of cancers, not just cervical."
Though the vaccine has been approved by the FDA, and according to Streicher, "is grounded in solid science," many conservative parents have opposed giving the vaccine to their preteen and teenage daughters, the target group for the vaccine.
"We don't need to be vaccinating children against something that can be prevented with a behavior change," said Kimberly Martinez, executive director of the Abstinence Clearinghouse, a nonprofit group that advocates teaching children not to have sex rather than to have safe sex.
"We have to teach kids values and boundaries," she said. "If you give kids the vaccine, you're giving them a license to go have sex. It's like if you teach a kid to use a condom, you know what they're going to do with it," she said.
Maria McKnight, a mother of two from Tea, S.D., said the risk of lung cancer, like the risk of cervical cancer, does not change her opposition to vaccinating her 7-year-old daughter.
"HPV is completely 100 percent preventable. I don't see the point of putting her through the risk of the vaccine," she said. "In the same way I protect my kids from lung cancer by teaching them not to smoke or do drugs, I can protect them from HPV by teaching them not to have sex."
"I'd love to see cervical cancer wiped off the planet," she said. "I've watched someone die of lung cancer and would love to see that gone too. But we're talking about stopping a sexually transmitted disease. Stopping the behavior is the best way to stop the disease."
If HPV is increasingly linked with other forms of cancer and the vaccine becomes available to boys, McKnight said she would not give her 11-year-old son the vaccine for the same reasons.
Some parents remain opposed to the vaccine, citing side effects and fears that it has not been tested thoroughly enough to know its long-term effects. When the vaccine was initially introduced, some states attempted to pass legislation making it required for children to enter school. Only Virginia has passed a law mandating the vaccine, which will go into effect next October.
Physicians who advocate for the vaccine said concerns about premarital sex should not trump health.
"Whether or not HPV is associated with sex is irrelevant," Streicher said. "Anyone opposed to the vaccine doesn't understand it, or has an agenda. The vaccine is grounded in solid science."