National Cancer Institute

What are human papillomaviruses, and how are they transmitted?

Human papillomaviruses (HPVs) are a group of more than 150 related viruses. They are called papillomaviruses because certain types may cause warts, or papillomas, which are benign (noncancerous) growths.

Some HPVs, such as those that cause the common warts that grow on the hands and feet, do not spread easily. However, more than 40 HPV types can be sexually transmitted, and these HPVs spread very easily through genital contact. Some types of sexually transmitted HPVs cause cervical cancer and other types of cancer (1). These are called high-risk, oncogenic, or carcinogenic HPVs. Other sexually transmitted types of HPV do not appear to cause cancer and are called low-risk HPVs.

Although genital HPV infections are very common, most occur without any symptoms and go away without any treatment within a few years. However, some HPV infections can persist for many years. Persistent infections with high-risk HPV types can cause cell abnormalities. If untreated, areas of abnormal cells, called lesions, can sometimes develop into cancer.

What are genital warts?

Some types of sexually transmitted low-risk HPVs cause warts to appear on or around the genitals or anus. Most genital warts (technically known as condylomata acuminata) are caused by two HPV types, HPV-6 and HPV-11. Warts may appear within several weeks after sexual contact with a person who is infected with HPV, or they may take months or years to appear, or they may never appear.

What is the association between HPV infection and cancer?

Persistent HPV infections are now recognized as the cause of essentially all cervical cancers, as well as most cases of anal cancer. In 2011, more than 12,000 women in the United States are expected to be diagnosed with cervical cancer and more than 4,000 are expected to die from it (2). Cervical cancer is diagnosed in nearly half a million women each year worldwide, claiming a quarter of a million lives annually.

Although anal cancer is uncommon, more than 5,000 men and women in the United States are expected to be diagnosed with the disease in 2011, and 770 people are expected die from it (2).

Genital HPV infection also causes some cancers of the vulva, vagina, and penis (3). In addition, oral HPV infection causes some cancers of the oropharynx (the middle part of the throat, including the soft palate, the base of the tongue, and the tonsils) (3, 4).

It has been estimated that HPV infection accounts for approximately 5 percent of all cancers worldwide (3).

Are specific types of HPV associated with cancer?

Both high-risk and low-risk types of HPV can cause the growth of abnormal cells, but only the high-risk types of HPV lead to cancer. It is important to note that the great majority of infections with high-risk HPV types go away on their own and do not cause cancer (5).

At least 15 high-risk HPV types have been identified, including HPV types 16 and 18. These two types of HPV together cause about 70 percent of all cases of cervical cancer (5, 6). In addition, infection with high-risk HPVs, mainly HPV type 16, causes about 85 percent of anal cancers (7).

Some oropharyngeal cancers are also caused by HPV infection—almost exclusively by HPV 16 (8). The proportion of oropharyngeal cancers caused by HPV is likely to vary according to geographic region. Studies are under way to evaluate this question.

What are the risk factors for HPV infection and cervical cancer?

Having many sexual partners is a risk factor for HPV infection. Nevertheless, most HPV infections go away on their own without causing any type of abnormality. However, even among women who develop abnormal cervical cell changes because of persistent infection with high-risk HPV types, the chances of developing cervical cancer are small, even if the abnormal cells are not treated. As a general rule, the more severe the abnormal cell changes, the greater the risk of cancer.

Whether an HPV-infected woman develops cervical cancer appears to depend on a variety of factors acting together with infection by high-risk HPV types. Factors that may increase the risk of cervical cancer in women persistently infected with high-risk HPV types include smoking and having many children (5).

Can HPV infection be prevented?

The surest way to eliminate risk for genital HPV infection is to refrain from any genital contact with another individual (1). For those who are sexually active, a long-term, mutually monogamous relationship with an uninfected partner is the strategy most likely to prevent HPV infection (1). However, it is difficult to determine whether a partner who has been sexually active in the past is currently infected.

Research has shown that correct and consistent condom use can reduce the transmission of HPV between sexual partners (9). However, because areas not covered by a condom can be infected by the virus (1), condoms are unlikely to provide complete protection against transmission of infection.

The Food and Drug Administration (FDA) has approved two vaccines to prevent HPV infection: Gardasil® and Cervarix®. Both vaccines are highly effective in preventing infections with HPV types 16 and 18, two high-risk HPVs that cause about 70 percent of cervical and anal cancers. Gardasil also prevents infection with HPV types 6 and 11, which cause 90 percent of genital warts (10). More information on this topic is available in the NCI fact sheet Human Papillomavirus (HPV) Vaccines ¹.

How are cervical HPV infections detected?

Cervical cells can be tested to identify high-risk types of HPV that may be present. HPV DNA tests look for viral DNA from multiple high-risk HPV types and can detect the presence of a viral infection before any cell abnormalities become visible. The FDA has approved HPV DNA tests for follow-up testing of women with equivocal cell abnormalities on a Pap test (a screening test to detect cervical cell changes). HPV DNA tests are also approved for general cervical cancer screening of women over age 30 when done together with a Pap test. There are currently no approved tests to detect HPV infections in men.

What are the treatment options for HPV infection?

Although there is currently no medical treatment for HPV infections, the cervical lesions and warts that can result from such infections can be treated. Methods commonly used to treat cervical lesions include cryosurgery (freezing that destroys tissue), LEEP (loop electrosurgical excision procedure, or the removal of tissue using a hot wire loop), and conization (surgery to remove a cone-shaped piece of tissue from the cervix and cervical canal). Similar treatments may be used for external genital warts. In addition, some drugs may be used to treat external genital warts (11). More information about treatment for genital warts can be found in the Centers for Disease Control and Prevention (CDC) Sexually Transmitted Diseases Treatment Guidelines, 2010 ².

How can people learn more about HPV infection?

The following federal government agencies can provide more information about HPV infection:

• The National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health, supports research on HPV infection and offers printed materials. NIAID can be contacted at:
  
  

  Organization:	National Institute of Allergy and Infectious Diseases
  Address:	Office of Communications and Government Relations 6610 Rockledge Drive, MSC 6612 Bethesda, MD 20892–6612
  Telephone:	301–496–5717 1–866–284–4107 (toll-free)
  TTY:	1–800–877–8339
  E-mail:	ocpostoffice@niaid.nih.gov
  Website:	http://www.niaid.nih.gov/Pages/default.aspx

  
  
• The CDC, part of the Department of Health and Human Services, also offers support and information about HPV.

  • The CDC-INFO Contact Center provides information about sexually transmitted infections, including HPV, and how to prevent them. The center can be reached by calling toll-free 1–800–CDC–INFO (1–800–232–4636). Both English- and Spanish-speaking specialists are available from 8:00 a.m. to 8:00 p.m. Eastern Time, Monday through Friday. The center can also be reached by e-mail at cdcinfo@cdc.gov. Staff provide information about sexually transmitted diseases and referrals to free or low-cost clinics nationwide.

  • Free educational literature about sexually transmitted infections and prevention methods is also available from the CDC ³.

  • The CDC also makes information about HPV, including treatment guidelines and surveillance statistics, available on its Human Papillomavirus (HPV) ⁴ Web page.