The Virus That Causes Cervical Cancer

<< Back to Articles

> PDF Version

Health Monitor

The human papillomavirus (HPV) is the most common sexually transmitted virus in the U.S. About 80% of women who have been sexually active carry it at some time. In most women, however, the virus is cleared — or at least held in check — by the immune system. But monitoring its presence is key to keeping a persistent HPV infection from damaging cervical tissue, at the lower end of the uterus, and potentially causing cancer. About 30 different types of HPV are sexually transmitted. Some cause genital warts, or papillomas. About 15 types are termed "high-risk" because they can cause changes that may lead to cancer.

Who's at risk?
The number of sexual partners that a woman has over her lifetime is the most significant risk factor for HPV infection. Having sex with someone who has had a number of partners also heightens that risk. So does youth: HPV prevalence increases during the years women start to become sexually active and are exposed to the virus for the first time. It declines with age because older women tend to have fewer sexual partners and acquire immunity to the virus. Using condoms reduces but doesn't eliminate the risk of infection; the virus can be transmitted by contact with skin not covered by a condom.

HPV is common— cancer is not
Studies indicate that among young women, 70% of new HPV infections disappear within 12 months, and 91% are gone within 2 years. It takes a long time — an estimated 10 to 15 years-for a woman with persistent HPV infection to go from the stage of being a carrier with no symptoms to the stage in which cell changes that precede cervical cancer occur.

Detection
Genital warts are a giveaway that HPV has invaded. But because the virus often produces no symptoms, women need to be screened with Pap tests. In this procedure, cells are scraped from the cervix and examined under a microscope for abnormalities. Cells are graded according to how far they have progressed along the path toward cancer. Pap tests, however, miss a significant percentage of suspicious changes. But, doctors can now call upon a test that requires a cervical swab to identify high-risk types of HPV by their DNA.

The Pap plus HPV testing — a winning combination
The more sensitive HPV test combined with regular Pap tests is nearly 100% effective in detecting HPV in the most at-risk population of women 30 and older. (Routine HPV screening for women under 30 is not recommended because at that age HPV infections are common and usually disappear over time.) If a woman tests positive for HPV but her Pap result is normal, it's recommended that she be re-tested using both methods in 6 months to a year. A woman with a positive HPV test and an abnormal Pap result will require a colposcopy. In this procedure, a doctor uses a magnifying device to examine the cervix; the doctor may also remove a small sample of tissue for testing in a lab.

An HPV vaccine
A new vaccine, called Gardasil, immunizes against 2 strains of the virus-HPV-16 and HPV-18-which together are responsible for 70% of cervical cancers. A vaccine that can protect against these strains of HPV could prevent most cervical cancer and potentially save thousands of lives. Gardasil also protects against 2 strains that cause genital warts. Three doses are administered over a period of 6 months. To be most effective, the vaccine should be given before a woman becomes sexually active. However, any woman younger than 27 years is a candidate. Experts caution that because not all potentially cancer-causing strains of HPV are covered by the vaccine, vaccinated women will still need to be screened for cervical cancer.