What is the connection between HPV and cancer?
Human papillomavirus (HPV) is 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.
When a woman is exposed to HPV, her immune system usually prevents the virus from doing any harm. But in a small number of women, the virus survives for years and eventually converts some cells on the surface of the cervix into cancer cells. These changes happen very slowly.
At first, the cells only show signs of a viral infection. Later, the cells become precancerous. In time, it progresses to invasive cervical cancer.
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).
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. 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.
How can HPV and cancer be detected?
Genital warts or HPV viruses are sometimes detected during your annual gynecological examination, although the Pap test is not a screening tool for HPV or any other STD or infection. Although most HPVs do not progress to cancer, it is especially important for women diagnosed with HPVs to have regular Pap test.
While the Pap test is not designed to detect HPV (only abnormal cervical changes) abnormal changes may indicate HPV infection or another vaginal infection. Your physician will either order follow up screening procedure such as a colposcope or follow you closely to detect any further cervical changes when abnormal Pap results are obtained.
If your Pap test result indicates dysplasia--it's important to note that cervical dysplasia does not mean cervical cancer. However cervical dysplasia is thought to be a precursor condition for carcinoma in situ (CIS) (also not cancer but a severe form of dysplasia) and invasive cancer of the cervix. Many cases of dysplasia regress over time, and the factors that lead to progression to invasive cervical cancer remain unclear.
In CIS, an outer layer of normal cells is replaced by cancer cells. CIS is about 95% treatable and curable. Invasive cancer of the cervix occurs when cancer cells have invaded the underlying tissues of the cervix. CIS occurs generally in women between 25 and 34 while invasive cancer of the cervix primarily occurs in women over the age of fifty.
The prognosis for invasive cervical cancer is largely dependent on the extent of disease at the time of initial diagnosis. The current death rate for cervical cancer remains higher that it should be due to the approximately one-third of women who do not have regular annual Pap smears. An estimate 90% of cervical cancer deaths could be eliminated through earlier detection with the Pap smear.
Who is most likely to get cancer from HPV?
It's not clear why some women are more likely to develop cervical cancer. Some types of HPV are more aggressive than others and that plays a role. Cigarette smoking increases the risk of both precancerous changes and cancer of the cervix. The best way to prevent sexually transmitted infections is to have fewer sexual partners and to always use condoms.
Sources: Division of STD Prevention. Prevention of genital HPV infection and sequelae: Report of an external consultants' meeting. Atlanta, GA: Centers for Disease Control and Prevention, 1999.