Thus, as Americans have expanded their sexual repertoire, as an October study from The Journal of Sexual Medicine highlighted, prevalence of HPV can sweep quickly through a population—especially one that is unprotected by a vaccine or consistent condom use.
With the increase in oropharyngeal cancer in particular, researchers have concluded that the disease stems from local infection acquired during sexual activity. "We think it's probably because of getting involved with oral sex at an earlier age than earlier generations," says Shanthi Marur, an assistant professor of oncology at Johns Hopkins Medicine's Upper Aerodigestive Cancer Program, who co-authored an August paper on the subject in The Lancet Oncology. Adults who are presenting with HPV-positive oral cancers likely contracted the virus in their teens and 20s, she notes.
Although heterosexual men seem to be at higher risk for HPV-positive oropharyngeal cancers (likely, researchers posit, because the virus tends to infect—and persist in—the genital area of female partners), men who have sex with men face an increased risk for HPV anal cancer. And for patients who have compromised immune systems, such as those with HIV or AIDS, "the risk of anal cancer is enormously high," Chaturvedi says.
And for anal, oral and other cancers, "we don't have a pap smear equivalent," Gillison says. So doctors are often left in the dark while a patient's infection turns cancerous and that cancer grows. For oral cancers, for example, she explains, "most of these cancers arise from deep within the tonsillar crypt," where visual detection is largely impossible until a sizable tumor has already formed.
Despite HPV's role in increasing the number of oropharyngeal cancers, it seems to produce tumors that are much easier to treat than HPV-negative malignancies.
"The HPV status of a patient's tumor is the biggest determining factor of whether they're going to live or die from that cancer," Gillison says. Two patients that present with otherwise identical tumors could have very different outcomes if one turns out to be HPV-positive. Someone with an HPV-negative tumor who was a heavy smoker has only about a 30 percent chance of being alive five years later, she explains. On the other hand, someone who has not smoked and presents with a tumor that turns out to be HPV-positive, "that person is expected to survive," Gillison says. In fact, she says, they have about a 95 percent chance of surviving the cancer for at least five years.
Researchers are still piecing together why the two forms of cancer have such different mortality rates, but Hartig suggests that it might have something to do with the degree of genetic mutations that have been detected in cancerous cells. "The genome of these cancer cells is less abnormal as compared to cancers caused by tobacco and alcohol, where there are even more mutations present," he says.
And the susceptibility of these HPV-positive cancers to standard radiation therapy has led many researchers and clinicians to wonder "if we can dial down treatment" for this set of patients, Marur says. A reduction in harsh radiation therapy could be a big deal for many HPV-positive oral cancer patients, especially as they tend to be much younger (often in their 40s and 50s) compared with the previous majority of patients whose malignancies are linked to smoking or alcohol consumption. "Perhaps we can do less [treatment] there and give our patients better quality of life," Hartig says.
Stopping the spread
The advent of the HPV vaccine, originally developed to prevent cervical cancer, offers some promise for stemming the spread of other HPV-related cancers in the future. Most oropharyngeal cancers are caused by HPV subtype 16, which is included in the vaccine. Only about a quarter of U.S. girls, however, have received even one of the three shots in the vaccine course. And the CDC is still debating whether to recommend the vaccine for boys as well. (Gardasil is currently approved for boys, about 1 percent of whom have been vaccinated.)
The key to slowing the spread of the virus via vaccines, though, is to immunize individuals before they become sexually active. "Vaccination prior to sexual debut is definitely the best recommendation," Chaturvedi says. And that effort will likely take more education.
As more people and parents learn about the virus, how it can be spread, and its link to cancer, Gillison says, "that might open up a little bit more conversation" about sexual behaviors and getting vaccinated at an earlier age—before sexual interactions, or even kissing, start. But, as she has observed in her own practice, "most patients we talk to who have HPV-associated head and neck cancers had no idea what HPV was."