A well-proven way to prevent cervix cancer is to have testing (screening) to find pre-cancers before they can turn into invasive cancer. The Pap test (sometimes called the Pap smear) and the HPV (human papilloma virus) test are the tests used for this. If a pre-cancer is found, it can be treated, stopping cervical cancer before it really starts. Since no HPV vaccine provides complete protection against all of the HPV types that can cause cancer of the cervix, it cannot prevent all cases of cervical cancer. This is why it is very important that women continue to have Pap tests, even after they’ve been vaccinated. Most invasive cervical cancers are found in women who have not had regular Pap tests.
The American Cancer Society recommends the following guidelines for early detection:
Some women believe that they can stop cervical cancer screening once they have stopped having children. This is not correct. They should continue to follow American Cancer Society guidelines.
Although annual (every year) screening should not be done, women who have abnormal screening results may need to have a follow-up Pap test done in 6 months or a year.
The American Cancer Society guidelines for early detection of cervical cancer do not apply to women who have been diagnosed with cervical cancer. These women should have follow-up testing as recommended by their healthcare team.
The Papanicolaou (Pap) test
The Pap test is the main screening test for cervical cancer and pre-cancerous changes.
Although the Pap test has been more successful than any other screening test in preventing a cancer, it is not perfect. One of the limitations of the Pap test is that it needs to be examined by humans, so an accurate analysis of the hundreds of thousands of cells in each sample is not always possible. Engineers, scientists, and doctors are working together to improve this test. Because some abnormalities may be missed (even when samples are looked at in the best laboratories), it is not a good idea to have this test less often than American Cancer Society guidelines recommend.
Pelvic exam versus Pap test
Many people confuse pelvic exams with Pap tests. The pelvic exam is part of a woman's routine health care. During a pelvic exam, the doctor looks at and feels the reproductive organs, including the uterus and the ovaries and may do tests for sexually transmitted disease. Pap tests are often done during pelvic exams, but you can have a pelvic exam without having a Pap test. A pelvic exam without a Pap test will not help find abnormal cells of the cervix or cervical cancer at an early stage.
The Pap test is often done at the start of the pelvic exam, after the speculum is placed. To do a Pap test, the doctor removes cells from the cervix by gently scraping or brushing it with a special instrument. Pelvic exams may help find other types of cancers and reproductive problems, but a Pap tests is needed to find early cervical cancer or pre-cancers.
How the Pap test is done
Cytology is the branch of science that deals with the structure and function of cells. It also refers to tests to diagnose cancer and pre-cancer by looking at cells under the microscope. The Pap test is a procedure used to collect cells from the cervix for cervical cytology testing.
The health care professional first places a speculum inside the vagina. The speculum is a metal or plastic instrument that keeps the vagina open so that the cervix can be seen clearly. Next, using a small spatula, a sample of cells and mucus is lightly scraped from the exocervix (see illustration in “What is cervical cancer?” section). A small brush or a cotton-tipped swab is then inserted into the opening of the cervix to take a sample from the endocervix (see illustration in “What is cervical cancer?” section). The cell samples are then prepared so that they can be examined under a microscope in the laboratory. This this is done in 2 main ways.
Conventional cytology: One way is to smear the sample directly onto a glass microscope slide, which is then sent to the laboratory. For about 50 years, all cervical cytology samples were handled this way. This method works quite well and is relatively inexpensive, but it does have some drawbacks. One problem with this method is that the cells smeared onto the slide are sometimes piled up on each other, making it hard to see the cells at the bottom of the pile. Also, white blood cells (pus), increased mucus, yeast cells, or bacteria from infection or inflammation can hide the cervical cells. Another problem with direct smears is that if the slides are not treated with a preservative right away, the cells can dry out. This can make it difficult to tell if there is something wrong with the cells. If the cervical cells cannot be seen well (because of any of these problems), the test is less accurate, and it may need to be done again.
Liquid-based cytology: The other way is to put the sample of cells from the cervix into a special preservative liquid (instead of putting them on a slide directly). This is sent to the lab. Technicians then use special lab instruments to spread some of the cells in the liquid onto glass slides to look at under the microscope. This method is called liquid-based cytology, or a liquid-based Pap test. The liquid helps remove some of the mucus, bacteria, yeast, and pus cells in a sample. It also allows the cervical cells to be spread more evenly on the slide and keeps them from drying out and becoming distorted. Cells kept in the liquid can also be tested for HPV. Using liquid-based testing may reduce the chance that the Pap test will need to be repeated, but it does not seem to find more pre-cancers than a regular Pap test. The liquid-based test is also more likely to find cell changes that are not pre-cancerous but that will need to be checked out further -- leading to unnecessary tests. This method is more expensive than a usual Pap test.
Another way to improve the Pap test is by using computerized instruments that can spot abnormal cells in Pap tests. A machine that can read Pap tests has been approved by the FDA to read Pap tests first (instead of them being examined by a technologist). It is also approved by the FDA for rechecking Pap test results that were read as normal by technologists. Any smear identified as abnormal by the machine would then be reviewed by a doctor or a technologist.
Computerized instruments can find abnormal cells that technologists sometimes miss. Most of the abnormal cells found this way are in rather early stages, such as atypical squamous cells (ASCs), but sometimes high-grade abnormalities missed by human testing can be found. Scientists do not know yet whether the instrument can find enough high-grade abnormalities missed by human testing to have a real impact on preventing invasive cervical cancers. Automated testing also increases the cost of cervical cytology testing.
For now, the best way to detect cervical cancer early is to make certain that all women are tested according to American Cancer Society guidelines. Unfortunately, many of the women most at risk for cervical cancer are not being tested often enough or at all.
Making your Pap tests more accurate
You can do several things to make your Pap test as accurate as possible:
Is there a Pap test you can do at home?
Doctors have been trying to find ways to get more women involved in cervical cancer screening. Some have proposed methods that would allow women to take cervical cell samples at home. For this test, a woman would collect cervical cells herself by inserting a small plastic applicator into the vagina and moving it around on the cervix. This would be placed in a special container to preserve the cells. Women in poorer countries have used this method to check for sexually transmitted diseases, and it has also been useful to check for HPV infections. So far, however, no "home-based" Pap test has been approved for use in the United States. Currently, the American Cancer Society does not recommend any “at-home” Pap test.
How Pap test results are reported
The most widely used system for describing Pap test results is the Bethesda System (TBS). There are 3 main categories, some of which have sub-categories:
Negative for intraepithelial lesion or malignancy: This first category means that no signs of cancer, pre-cancerous changes, or other significant abnormalities were found. Some specimens in this category appear entirely normal. Others may have findings that are unrelated to cervical cancer, such as signs of infection with yeast, herpes, or Trichomonas vaginalis (a microscopic parasite), for example. Specimens from some women may also show "reactive cellular changes", which is the way cervical cells respond to infection or other irritation.
Epithelial cell abnormalities: The second category, epithelial cell abnormalities, means that the cells lining the cervix or vagina show changes that might be cancer or a pre-cancerous condition. This category is divided into several groups for squamous cells and glandular cells. The epithelial cell abnormalities for squamous cells are:
Atypical squamous cells (ASCs): This term is used when there are cells that look abnormal, but it is not possible to tell (by looking at the cells under a microscope) if this is caused by infection, irritation, or is a pre-cancer. This group is further divided into 2 groups, atypical squamous cells of uncertain significance (ASC-US) and atypical squamous cells where high-grade squamous intraepithelial lesion (SIL) can’t be excluded (ASC-H). Most of the time, cells labeled ASC-US are not pre-cancer. Some doctors will recommend repeating the Pap test in 6 months. Some doctors use the HPV DNA test to help them decide whether or not to do a colposcopy. If a high-risk type of HPV is found, the doctor is more likely to order a colposcopy. (Colposcopy is discussed in more detail in the section, "Other tests for women with abnormal cervical cytology results.")
If the results of a Pap test are labeled ASC-H, it means that a SIL is suspected. Colposcopy is then recommended.
Squamous intraepithelial lesions (SILs): These abnormalities are subdivided into low-grade SIL and high-grade SIL. In low-grade SIL, the cells are mildly abnormal, while in high-grade SIL, the cells are severely abnormal. High-grade SILs are less likely than low-grade SILs to go away without treatment. They are also more likely to eventually develop into cancer if they are not treated. Treatment can cure most SILs and prevent true cancer from developing. A Pap test cannot tell for certain whether a woman has a high- or low-grade SIL. It merely fits the result into one of these abnormal categories. All patients over the age of 20 with a Pap test result of SIL should have colposcopy. The need for treatment is based on the results of the biopsies done at colposcopy. Since most SILs are positive for HPV, HPV testing is not used to decide if a woman with SIL results on a Pap test needs a colposcopy.
Pap testing is not recommended for women 20 years old or younger, but if they do have a Pap test that shows low-grade SIL, they should have a repeat Pap test in a year. If they have a high-grade SIL, colposcopy is recommended.
Squamous cell carcinoma: This result means that the woman is likely to have an invasive cancer. Further testing will be done to be sure of the diagnosis before treatment can be planned.
The Bethesda System also describes epithelial cell abnormalities for glandular cells.
Adenocarcinoma: Cancers of the glandular cells are called adenocarcinomas. In some cases, the pathologist examining the cells can tell whether the adenocarcinoma started in the endocervix, in the uterus (endometrium), or elsewhere in the body.
Atypical glandular cells: When the glandular cells do not look normal, but have features that do not permit a clear decision as to whether they are cancerous, the term used is atypical glandular cells (AGCs). The patient should have more testing if her cervical cytology result shows atypical glandular cells.
Other malignant neoplasms: This category is for forms of cancer that only rarely affect the cervix, such as malignant melanoma, sarcomas, and lymphoma.
Other descriptions of Pap test results have also been used in the past.
The HPV DNA test
As mentioned earlier, the most important risk factor for developing cervical cancer is infection with HPV. Doctors can now test for the types of HPV (high-risk or carcinogenic types) that are most likely to cause cervical cancer by looking for pieces of their DNA in cervical cells. The test is done similarly to the Pap test in terms of how the sample is collected, and it sometimes can even be done on the same sample.
The HPV DNA test can be used in 2 situations:
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