What is cervical cancer screening?
Cervical cancer develops in the narrow portion at the lower end of the uterus, where it joins the top of the vagina. Doctors find human papillomavirus (HPV) in around 99% of cervical cancers, although most cases of HPV do not become cancerous. Having HPV is the most significant risk factor for cervical cancer.
The Pap test and HPV test are the chief components of cervical cancer screening.
According to the National Cancer Institute, regular screening reduces the risk of developing or dying from cervical cancer by 80%.
The number of deaths from cervical cancer in the United States is declining by around 2% each year due to progress in testing and treatment.
In this article, we look at how a pap test works, who should receive a screening, and how to interpret the results.
Cervical cancer screening can involve testing for HPV or using the Pap test. The doctor may also carry out a physical examination of the pelvis at the same time.
Regular screenings can help detect and prevent cervical cancer.
A healthcare professional widens the vagina using a tool they call a speculum to allow access to the cervix. They then collect a sample of cells from the cervix. They will send the cell sample to a laboratory for examination under a microscope.
The laboratory technicians look at the appearance of the cells. If they appear abnormal, it may be a sign that cervical cancer is in the early stages of development, known as precancer.
Early treatment can correct these cellular changes and prevent the onset of cervical cancer.
A doctor will use the HPV test to detect the virus behind many abnormal cellular changes that could lead to cervical cancer.
However, the HPV DNA test may identifiy several infections that experts do not link to cancer. A positive HPV test often does not mean that a person will go on to develop cancer.
Screening criteria and guidelines
The American Cancer Society provide guidelines for regular cervical cancer screenings in females of all ages.
Between these ages, a woman should undergo Pap tests at 3-year intervals. HPV testing is not necessary at this stage. However, a doctor may follow up a Pap test with HPV testing if results are abnormal.
In one study, 86.7% of those who tested positive for HPV did not develop cancer in at least the following 10 years.
Doctors recommend the following for people of these ages:
- co-testing, or a combination of both tests, every 5 years
- a Pap test every 3 years
The American Cancer Society warn that a combined HPV and Pap test can lead to more false positives, more testing, and more invasive procedures.
Over 65 years
Women who have had regular screening in the last 10 years with clear results throughout can stop screening at this age.
However, if a test within the last 20 years has shown signs of a serious precancer, screening should continue until 20 years after this precancer finding.
Women with a high risk of cervical cancer
Women who have received an HPV vaccine should still undergo cervical cancer screenings.
Those who have a raised risk of cervical cancer should receive more frequent testing.
This includes females with a suppressed immune system, such as those with HIV or a previous organ transplant. People might also have a high risk if they had exposure to diethylstilbestrol (DES), a synthetic form of estrogen, before birth.
After a total hysterectomy, which involves removal of the uterus and cervix, screening is no longer necessary. However, if a doctor performed the hysterectomy to treat cancer, screening should continue.
Females who have received an HPV vaccination should still undergo screenings.
A person who has current or previous cervical cancer or precancer will have their own screening and treatment plan, as well as those with HIV infection.
A false positive result may not only cause stress but can lead to unnecessary procedures that may have long-term risks. For this reason, doctors do not recommend yearly screenings.
Cervical screening test results can be normal, unclear, or abnormal.
Normal: There were no changes in the cells of the cervix.
Unclear: The cells look like they could be abnormal, and the pathologist could not identify changes that could indicate precancer. These abnormal cells could relate to HPV, an infection, pregnancy, or life changes.
Abnormal: The lab technicians found changes in the cervical cells. Abnormal cells do not always indicate cancer. The doctor will often request further tests and treatment to see if the changes are becoming cancerous.
In an unclear result, cell changes have occurred, but the cells are very near normal and are likely to resolve without treatment. The doctor will likely request a repeat test within 6 months.
Younger people are more susceptible to low-grade squamous intraepithelial lesions (LSIL) that often resolve without treatment.
Cervical erosion, which doctors sometimes refer to as an ectropion, may also lead to an unclear result. Cervical erosion means that the cells of underlying glands can be seen on the surface of the cervix.
Erosions are common, especially among those individuals who are using the contraceptive pill, teenagers, or someone who is pregnant. Slight bleeding might also occur after sex.
Most cases of erosions resolve without treatment.
What to do after abnormal results
If a healthcare professional finds abnormal cells in the cervix, they may suggest further testing.
An abnormal result means that the pathologist detected changes in the person's cervix. This result does not necessarily mean that the individual has cervical cancer. In most cases, there is no cancer.
The abnormal changes in the cervical cells are often due to HPV. Low-grade changes are minor while high-grade changes are more serious. Most low-grade changes resolve without treatment.
It normally takes 3–7 years for "high-grade," or severe, abnormalities to become cervical cancer.
Cells showing more serious changes may eventually become cancerous unless a doctor removes them. Early intervention is vital for treating cervical cancer.
Doctors will need to do further tests to confirm abnormal Pap or HPV test results.
Rarely, test results might indicate the presence of cervical intraepithelial neoplasia (CIN). This term means that the screening found precancerous cells, but not that the individual has cervical cancer.
The results may show the following:
- CIN 1 (mild cell changes): One-third of the thickness of the skin that covers the cervix has abnormal cells.
- CIN 2 (moderate cell changes): Two-thirds of the thickness of the skin that covers the cervix has abnormal cells.
- CIN 3 (severe cell changes): All the thickness of the skin that covers the cervix has abnormal cells.
A doctor will need to confirm these results by requesting a biopsy.
While both standard cervical screening tests are often reliable and effective, unclear or abnormal results may reflect a problem with the examination rather than the presence of changing cells.
A person may have to repeat the test due to an "inadequate" sample, meaning that their results were inconclusive.
An inadequate sample could be due to:
- too few cells being available from the test
- the presence of an infection that obscures the cells
- menstruation, which can make viewing the cells hard
- inflammation of the cervix, which may obstruct the visibility of the cells
An individual looking to undergo cervical cancer screening should first take measures to manage infections or inflammation in the cervix.
The medically recommended tests for cervical cancer are the Pap test and HPV test. These tests show either changes in the cells or the presence of the HPV virus that suggest a higher risk of cervical cancer.
Screening is often highly effective and can allow for early treatment. However, results may be unclear and require further testing.
Females over the age of 21 years should receive a Pap test every 3 years.
Screening may be costly. However, many insurers provide coverage for testing. People without access to cervical cancer screening may use this facility to work out if they qualify for free testing under the National Breast and Cervical Cancer Early Detection Program (NBCCEDP).