What is human papillomavirus (HPV)? HPV is actually a group of viruses with at least 70 different types. At least 30 of these types infect the cervix, and about 15 of these have been connected with cervical cancer. The cancer-associated types of HPV are called high-risk types. Both high-risk and low-risk types can cause abnormalities in the cervix, but it appears that abnormalities associated with high-risk HPV viruses turn more often into high-grade lesions or cancer. HPV-16 is the type most commonly found in precancerous and cancerous lesions, followed by HPV-18. In fact HPV-16 and 18, along with 11 other virus types, are responsible for 90 percent of HPV infections that result in HSIL, severe changes in cells lining the cervix, and cervical cancer.

Who is at risk for HPV infection? HPV infection is more common in younger age groups, particularly among women who are in their teens and late 20s. Because HPV is mainly spread through sexual contact, the greater the number of sexual partners the greater the risk. Women who become sexually active early, who have multiple sexual partners, and whose sexual partners have other partners are at increased risk. Nonsexual transmission is also possible. The virus often disappears, but viral DNA can be detected in cervical cells for years after infection.

Does HPV cause cervical cancer? Yes. Scientists have concluded that there is a causal relationship between HPV and cervical cancer. Scientists continue to study other factors that may also be required for the development of cancer, such as changes in the immune system.

Does infection with a cancer-associated type of HPV always lead to a precancerous condition or cancer? No. Most infections appear to go away on their own without causing any kind of abnormality. However, infection with cancer-associated HPV types may increase the risk that mild abnormalities, such as ASCUS (atypical squamous cells of undetermined significance) and LSIL (low-grade squamous intraepithelial lesions), will progress to more severe abnormalities, such as HSIL, or cervical cancer. With regular follow-up care by trained clinicians, women with precancerous cervical abnormalities should not develop invasive cervical cancer.

Do LSIL and HSIL ever develop in the absence of any HPV infection? Yes, but rarely. The cells in a vast majority of low-grade and high-grade cervical lesions have detectable HPV DNA. Researchers think that less than 10 percent of all LSIL and HSIL have no HPV DNA present.

For answers to additional questions concerning HPV, ALTS, and cervical or other cancers, contact the National Cancer Institute's Cancer Information Service at 1-800-4-CANCER.