October 2, 20102
What Is Cervical Cancer?
The cervix forms the opening to the uterus from the vagina. It is covered with two main types of cells: squamous cells, which cover the part of the cervix that extends into the vagina, and columnar cells, which line the cervical opening. Most cervical cancers develop close to where these two cell types come together, in an area called the transformation zone. Once cervical cancer develops, it can spread throughout the cervix to neighboring organs or to distant sites in the body.
Cancerous and precancerous changes in cervical cells are often first detected by a Pap test, wherein a sample of cells is removed from the cervix using a small wooden or plastic spatula and a brush. The cells are then examined under a microscope in a laboratory. If Pap test results are abnormal, a physician may perform a colposcopy, using a microscope called a colposcope to better see the cervix. The physician applies a mild vinegar solution to the cervix, which makes abnormal cells appear more white than pink. If abnormal areas are identified, the physician may remove samples of tissue so that the cells can be further evaluated—a procedure called a biopsy.
The results of the biopsy allow the physician to diagnose cancer or precancerous conditions. Precancerous changes to the cervix are called cervical intraepithelial neoplasia (CIN). The severity of CIN is graded on a scale of 1 to 3, with 3 being the most severe. CIN2 and CIN3 are considered “high-grade” CIN and may progress to cancer if not treated.
What Is HPV?
There are more than 100 different types of human papillomavirus (HPV), and different types of HPV cause different conditions. Some types of HPV are linked with common skin warts, others cause genital warts, and still others are linked with cancers of the cervix, vulva, vagina, penis, and anus as well as some cases of head and neck cancer. HPV types 6 and 11 account for a majority of cases of genital warts, and HPV types 16 and 18 cause roughly 70 percent of all cases of cervical cancer. The remaining cases of cervical cancer are linked with other high-risk types of HPV.
The types of HPV that cause genital warts or cervical cancer are transmitted sexually. Sexual transmission of HPV is extremely common and generally occurs soon after an individual becomes sexually active. Most infections resolve on their own, but others persist. Persistent infection with a high-risk type of HPV can lead to precancerous changes to the cervix and, if these changes are not treated, to cervical cancer.
How is HPV linked to Cervical Cancer?
The sexually transmitted types of HPV most commonly linked with cervical cancer are HPV 16 and HPV 18 (transmitted sexually), but several other high-risk types contribute to cancer as well.
Though a link between cervical cancer and a sexually transmitted infection was long suspected, studying HPV was historically a challenge because it could not be grown in cell or tissue cultures like some other organisms. It would take the molecular techniques that were introduced in the 1970s to adequately study and understand the virus. Once these techniques were applied, it became apparent that most cervical cancers contained evidence of HPV.
Infection with a high-risk type of HPV does not necessarily lead to cancer. Many infections disappear on their own, and others may persist without causing cancer. Infection does, however, increase the risk of cancer, and virtually all cases of cervical cancer can be linked to infection with a high-risk type of HPV.
Is There a Test for HPV?
The recognition that specific types of HPV are the cause of cervical cancer led to the development of tests to identify women infected with high-risk types of HPV. Information about HPV status may guide decisions about follow-up care.
HPV testing may also have a role in initial cervical cancer screening, but conclusive evidence about this is still lacking. In the meantime some organizations have supported the combination of HPV testing and Pap testing for screening women over the age of 30. Women who test negative for both tests may need not be rescreened for up to three years. The combination of HPV testing and Pap testing is not recommended for screening younger women because most will have HPV infections that will clear without causing precancerous cervical lesions.