Human Papillomaviruses and Cancer

by National Cancer Institute

Human papillomaviruses (HPVs) are a group of more than 100 types of viruses.

Most HPV infections go away on their own.

HPVs are the major cause of cervical cancer. HPVs may also play a role in cancers of the anus, vulva, vagina, and penis, and some cancers of the oropharynx.

Although there is no cure for HPV infection, the warts and lesions these viruses cause can be treated.

Researchers at the National Cancer Institute and elsewhere are conducting research on HPV-related cancers.

1. What are human papillomaviruses, and how are they transmitted?

Human papillomaviruses (HPV) are a group of more than 100 viruses. They are called papillomaviruses because certain types may cause warts, or papillomas, which are benign (noncancerous) tumors. The HPVs that cause the common warts which grow on hands and feet are different from those that cause growths in the throat or genital area. Some types of HPV are associated with certain types of cancer. These are called "high-risk" oncogenic or carcinogenic HPVs.

Of the more than 100 types of HPV, over 30 types can be passed from one person to another through sexual contact. Although HPVs are usually transmitted sexually, doctors cannot say for certain when infection occurred. Most HPV infections occur without any symptoms and go away without any treatment over the course of a few years. However, HPV infection sometimes persists for many years, with or without causing cell abnormalities.

2. What are genital warts?

Some types of HPV may cause warts to appear on or around the genitals or anus. Genital warts (technically known as condylomata acuminatum) are most commonly associated with 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. HPVs may also cause flat, abnormal growths in the genital area and on the cervix (the lower part of the uterus that extends into the vagina). However, HPV infections usually do not cause any symptoms.

3. What is the association between HPV infection and cancer?

HPVs are now recognized as the major cause of cervical cancer. In 2006, an estimated 10,000 women in the United States will be diagnosed with this type of cancer and nearly 4,000 will die from it. Cervical cancer strikes nearly half a million women each year worldwide, claiming a quarter of a million lives. Studies also suggest that HPVs may play a role in cancers of the anus, vulva, vagina, and some cancers of the oropharynx (the middle part of the throat that includes the soft palate, the base of the tongue, and the tonsils). Data from several studies also suggest that infection with HPV is a risk factor for penile cancer (cancer of the penis).

4. Are there specific types of HPV that are associated with cancer?

Some types of HPV are referred to as "low-risk" viruses because they rarely develop into cancer. HPV types that are more likely to lead to the development of cancer are referred to as "high-risk." Both high-risk and low-risk types of HPV can cause the growth of abnormal cells, but generally only the high-risk types of HPV may lead to cancer. Sexually transmitted, high-risk HPVs include types 16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 68, 69, and possibly a few others. These high-risk types of HPV cause growths that are usually flat and nearly invisible, as compared with the warts caused by types HPV-6 and HPV-11. It is important to note, however, that the majority of high-risk HPV infections go away on their own and do not cause cancer.

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

Having many sexual partners is a risk factor for HPV infection. Although most HPV infections go away on their own without causing any type of abnormality, infection with high-risk HPV types increases the chance that mild abnormalities will progress to more severe abnormalities or cervical cancer. Still, of the women who do develop abnormal cell changes with high-risk types of HPV, only a small percentage would develop cervical cancer if the abnormal cells were not removed. Studies suggest that whether a woman develops cervical cancer depends on a variety of factors acting together with high-risk HPVs. The factors that may increase the risk of cervical cancer in women with HPV infection include smoking and having many children.

6. 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.

For those who choose to be sexually active, a long-term, mutually monogamous relationship with an uninfected partner is the strategy most likely to prevent genital HPV infection. However, it is difficult to determine whether a partner who has been sexually active in the past is currently infected.

HPV infection can occur in both male and female genital areas that are covered or protected by a latex condom, as well as in areas that are not covered. Although the effect of condoms in preventing HPV infection is unknown, condom use has been associated with a lower rate of cervical cancer.

Recently, the U.S. Food and Drug Administration (FDA) approved a vaccine that is highly effective in preventing infection with types 16 and 18, two "high-risk" HPVs that cause most (70 percent) cervical cancers, and types 6 and 11, which cause most (90 percent) genital warts.

7. How are HPV infections detected?

Testing samples of cervical cells is an effective way to identify high-risk types of HPV that may be present. The FDA has approved an HPV test as a follow-up for women who have an ambiguous Pap test (a screening test to detect cervical cell changes and, for women over the age of 30, for general cervical cancer screening). This HPV test can identify 13 of the high-risk types of HPV associated with the development of cervical cancer. This test, which looks for viral DNA, is performed by collecting cells from the cervix and then sending them to a laboratory for analysis. The test can detect high-risk types of HPV even before there are any conclusive visible changes to the cervical cells. There are currently no tests approved to detect HPV infection in men.

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