The main cause of cervical cancer is infection with HPV. There are many types of HPV. Some types have been linked to cancer of the cervix, vulva, vagina, anus, and penis. Some also can cause cancer of the head and neck. These types of HPV are known as “high-risk” types. Most cases of cervical cancer are caused by just two high-risk types of HPV—type 16 and type 18. Cells that are infected with HPV appear different from normal cells under a microscope. Abnormal changes can be mild, or they can be more serious. The more serious changes can lead to cancer if not treated (see FAQ191 "Human Papillomavirus [HPV] Vaccination" ).