Human papillomavirus (HPV) is a large group of more than 150 related DNA viruses. HPV is named for the warts (papillomas) some types can cause and is spread through direct skin-to-skin contact. Although most HPV infections cause no symptoms and resolve spontaneously, some persist and result in warts or precancerous lesions. Of the more than 150 types, over 40 types are known to be transmitted through sexual contact and make it the most commonly sexually transmitted infection (STI).
HPV-induced cancers arise when viral sequences are integrated into the DNA of host cells. Some genes carried by the HPV virus, such as genes E6 and E7, act as oncogenes that promote tumor growth and malignant transformation. Roughly 12 HPV types (including 16, 18, 31, and 45) are classified as high-risk for being linked to malignancies. Nearly all cases of cervical cancer are associated with HPV infection, with two types present in 70% of cases: HPV16 and HPV18. Previous studies suggest that high-risk E7 oncoproteins are necessary for this cancer, by inactivating cell-cycle regulatory proteins. The ability to monitor these E7 levels may be a useful tool in cervical cancer screening and detection.