Cervical Cancer Screening
Margo Kerrigan, M.P.H., Area Director
Indian Health Service California Area Office
Cervical cancer screening is one of the success stories of cancer prevention. Although cervical cancer was once the leading cancer killer of women, it now ranks 13th in mortality among US women.
When found and treated early, cervical cancer often can be cured. It is usually a slow-growing cancer that may not have symptoms. It can be found with regular Pap tests, a procedure in which cells are scraped from the cervix and looked at under a microscope. The incidence of cervical cancer has declined 70% since the introduction of the Pap smear in 1941. A Pap smear can detect changes in the cervix before cancer develops and can find early cancer in its most curable stage. About half of all cervical cancers occur in women who have never had a Pap and between 60-80% of women found to have advanced cervical cancer have not had a Pap test in the previous five years.
American Indian and Alaska Native (AI/AN) women once had a very high rates of cervical cancer. In recent years, rates have declined, but still remain above national averages. A study conducted jointly between IHS, Centers for Disease Control and the American Cancer Society found that between 1999 and 2004, the overall cervical cancer rate for AI/AN women was approximately 25% higher than the rate for non-Hispanic white women. The death rate for AI/AN women was also higher.
One reason for a higher relative death rate among AI/AN women is that they are less likely to have a Pap test than other groups. AI/AN women are more likely than any other racial or ethnic group to report never having had a prior Pap screen, and they also have the highest proportion of abnormal first screens. Because of lower screening rates, AI/AN women with cervical cancer are less likely to have their cancers found at an earlier, more treatable stage. The 5-year relative survival rate for invasive cervical cancer caught at its earliest stage is almost 100%. By contrast, only 17% of those with an advanced stage of the disease will survive for 5 years. The American Cancer Society recommends that women should be screened every 1-2 years with a Pap test. Women over age 30 with three normal test results in a row may be screened every 2-3 years. Women with weak immune systems or HIV infections should be tested more often.
HPV and Cervical Cancer
The main risk factor for cervical cancer is infection by the Human Papilloma Virus (HPV). Most HPV infections will not lead to cervical cancer, but nearly 100% of women with cervical cancer have evidence of infection with HPV. HPV is a group 100 different types of viruses, of which over 30 are sexually transmitted. HPVs are classified into high, intermediate, and low-risk types. Types 16 and 18 are considered high-risk types and are associated with aggressive forms of cervical cancers. These two types cause up to 70% of all cervical cancers. The major risk factor for HPV infection is sexual behavior, including early age at onset of sexual activity, multiple sexual partners, failure to use barrier methods of contraception, and infection with other sexually transmitted diseases, particularly HIV. Genital HPV infection is especially common among sexually active young women under age 25. An study of the prevalence of HPV infection found that about 27% of women ages 14 to 59 tested positive for one or more strains of HPV.
The HPV DNA test can test for the types of HPV that are most likely to cause cervical cancer. The FDA has approved the HPV DNA for use as a screening test in combination with the Pap test in women over 30 years old. The HPV DNA test is not recommended as a screening test in women under 30 because the test is not as reliable in this population. The HPV DNA test can also be used in women with slightly abnormal Pap test results to determine if more testing or treatment is needed.
Preventing HPV Infection
However, for younger women, a new tool has been developed in the field of cervical cancer prevention. In June 2006, the US Food and Drug Administration (FDA) approved Gardasil®, a vaccine that prevents the most common HPV infections that cause cervical cancer (HPV-16 and HPV-18), for use in females aged 9-26. Studies have shown that the vaccine has the potential to prevent up to 70% of the invasive cervical cancers and cervical cancer deaths in the United States each year.
To be most effective, the HPV vaccine should be given before a girl becomes sexually active. The Federal Advisory Committee on Immunization Practices (ACIP) has recommended that the vaccine be routinely given to females aged 11 to 12 and as early as age 9, at the discretion of doctors. The committee also recommended females ages 13 to 26 who have not yet been vaccinated receive "catch-up" vaccinations. The HPV vaccine should be given in three doses within one year.
However, the HPV vaccine is not a replacement for a Pap test. The vaccine will not provide protection against all types of HPV that cause cervical cancer, and women may not receive the full benefits of the vaccine if they do not complete the vaccine series. Also, women may not receive the full benefits if they receive the vaccine after they have been infected with one or more HPV types. Thus, women of all ages should continue to receive regular cervical cancer screening, regardless of whether they have been vaccinated.
Government Performance and Results Act (GPRA)
The Indian Health Service has a GPRA measure relating to Cervical Cancer Screening. In FY 2008, IHS had a 59% pap screening rate for women ages 21-64. This rate includes women who have had a pap smear within the previous three years, which means that women ages 18-64 are included.
For More Information
American Cancer Society
Centers for Disease Control and Prevention
National Cancer Institute