The human papilloma virus (HPV) infects the lowest cell layer of the skin, the basement membrane. Here precancerous cells expand to the surface. For instance, condyloma (warts) are considered to be a form of mild dysplasia. These warts are not cancer, but they do indicate an HPV infection.
In addition to anal cancer, HPV infection is associated with other types of cancers, including cancers of the urinary system, sex organs, and head and neck. HPV infection is common. Most sexually active US adults will get HPV at some time in their lives.