High-risk HPVs are by far the most important factor in the development of cervical cancer. HPVs are DNA viruses that are grouped into those of high and low oncogenic risk based on their genotypes. There are 15 high-risk HPVs that are currently identified, but HPV-16 alone accounts for almost 60% of cervical cancer cases, and HPV-18 accounts for another 10% of cases; other HPV types contribute to less than 5% of cases, individually. High-risk HPVs are also implicated in squamous cell carcinomas arising at many other sites, including the vagina, vulva, penis, anus, tonsil, and other oropharyngeal locations. As noted earlier, low oncogenic risk HPVs are the cause of sexually transmitted vulvar, perineal, and perianal warts (condyloma acuminatum).