Some HPV types, such as HPV-5, may establish infections that persist for the lifetime of the individual without ever manifesting any clinical symptoms.
HPV types 1 and 2 can cause common warts in some infected individuals.
A wide variety of HPV types can cause genital warts, but types 6 and 11 together account for about 90% of all cases.
The International Agency for Research on Cancer has found that people with lung cancer were significantly more likely to have several high-risk forms of HPV antibodies compared to those who did not have lung cancer.
Researchers looking for HPV among 1,633 lung cancer patients and 2,729 people without the lung disease found that people with lung cancer had more types of HPV than noncancer patients did, and among lung cancer patients, the chances of having eight types of serious HPV were significantly increased.
HPV-associated cancers make up over 5% of total diagnosed cancer cases worldwide, and this incidence is higher in developing countries where it is estimated to cause almost half a million cases each year.
Some of the "early genes" carried by the HPV virus, such as genes E6 and E7, act as oncogenes that promote tumor growth and malignant transformation.
Most HPV infections of the cervix are cleared rapidly by the immune system and do not progress to cervical cancer (see below the Clearance subsection in Virology).
Because the process of transforming normal cervical cells into cancerous ones is slow, cancer occurs in people having been infected with HPV for a long time, usually over a decade or more (persistent infection).E6 also has a close relationship with the cellular protein E6-associated protein (E6-AP), which is involved in the ubiquitin ligase pathway, a system that acts to degrade proteins.E6-AP binds ubiquitin to the p53 protein, thereby flagging it for proteosomal degradation.In the United States, HPV is expected to replace tobacco as the main causal agent for oral cancer, and the number of newly diagnosed, HPV-associated head and neck cancers is expected to surpass that of cervical cancer cases by 2020.In recent years, the United States has experienced an increase in the number of cases of throat cancer caused by HPV type 16.Genital warts are quite contagious, while common, flat, and plantar warts are much less likely to spread from person to person.