Almost 45 percent of patients had had more than 10 sexual partners during their lifetimes, compared with 19 percent of the cancer-free controls. People under 23 who had a sexual partner at least 10 years older were more likely to be infected, possibly because older people have had longer exposure to the virus.
Deep kissing was also associated with increased risk. Those who had 10 or more deep-kissing partners were more than twice as likely to have an HPV-related cancer as those who had none or one.
People who reported that their partners had extramarital affairs, and those who even suspected that their partners had had affairs, also had an increased risk of HPV-associated throat cancer. There was no association of HPV-related throat cancer with smoking, alcohol consumption or substance use.
The study had limitations. It depended on self-reports, which are not always reliable, and because more than 95 percent of the participants described themselves as heterosexual, there was not enough data to draw conclusions about the effects of sexual orientation on HPV and cancer risk. But the analysis had carefully matched controls, HPV tumor data, and a confidential questionnaire, all of which contribute to its strengths.
Dr. Jason D. Wright, an associate professor of gynecologic oncology at Columbia who was not involved in the research, believes the work could be useful in clinical practice. “This is one of the first studies to provide in-depth details for patients about how specific practices influence your long-term risk,” he said. “A higher exposure, more partners, oral sex early on — these are all risk factors. These are important things to think about in talking to patients.”
The lead author, Dr. Virginia E. Drake, a resident physician at Johns Hopkins, said that explaining the infection to patients can be difficult. “If people get this infection, they’re going to ask, ‘Why me?’” she said. “How this information will change things clinically, we don’t know. But we can give patients a better understanding of the disease process and how someone gets it.”
Still, she said, “It’s complex, more complex that just the number of sexual partners. We don’t have the exact answers on this, and we’re still figuring out the complete picture.”