Cervical cancer screening is used to find changes in the cells of the cervix that could lead to cancer. The cervix is the opening to the uterus and is located at the top of the vagina. Screening includes cervical cytology (also called the Pap test or Pap smear) and, for some women, testing for human papillomavirus (HPV). Cancer occurs when cervical cells become abnormal and, over time, grow out of control. The cancer cells invade deeper into the cervical tissue. In advanced cases, cancer cells can spread to other organs of the body. Most cases of cervical cancer are caused by infection with HPV. HPV is a virus that enters cells and can cause them to change. Some types of HPV have been linked to cervical cancer as well as cancer of the vulva, vagina, penis, anus, mouth, and throat. Types of HPV that may cause cancer are known as "high-risk types."HPV is passed from person to person during sexual activity. It is very common, and most people who are sexually active will get an HPV infection in their lifetime. HPV infection often causes no symptoms. Most HPV infections go away on their own.