About 15 of the 100 strains of the virus may cause cancer, including some ovarian, cervical and uterine cancers. It's estimated that up to 35 percent of oral cancers, like the one Douglas has, is caused by strains of HPV. The virus usually is symptomless, though genital warts may be a visible symptom of HPV. The surprising news about HPV is that it's very, very common – in fact, up to 90 percent of sexually active people will be exposed to some form of the virus before age 25. The good news is that cancer obviously will not happen to every person who has the virus. More good news about HPV-related cancers is the fact that a vaccine exists to protect against cervical cancer for girls and genital warts for both girls and boys. Experts recommend the vaccine at age 11.