Cervical Screening Quality and Efficiency
Of the 44,744 women who had an abnormal Pap test result in 2015, 2,269 were diagnosed with pre-invasive cervical cancer, a positive predictive value (PPV) of 5.1%. The PPV of the Pap test in Ontario has increased over time, up from 4.7% in 2012 to 6.7% in 2014. The PPV for 2015 (5.1%) represents a decrease from the previous year.
Measure: Percentage of screen-eligible Ontario women, age 21 to 69, with an abnormal Pap test result who were diagnosed with a pre-invasive cervical lesion after a follow-up colposcopy or surgical procedure
As of this Report:
What is cervical screening?
- Cancer screening tests people who may be at risk of getting cancer, but who have no symptoms and generally feel fine. It is not meant to diagnose cancer. Instead, it helps determine which people are more likely to develop cancer in the future. Ontario operates organized screening programs for 3 types of cancer: breast, cervical and colorectal. The purpose of cervical screening is to prevent cervical cancer by identifying pre-cancerous changes in the cells of the cervix. In Ontario, the cervical screening test currently in use is the Pap test. Changes to the cervical screening test are under consideration.
- Cancer Care Ontario updated its cervical screening guidance in 2012. It now recommends cervical screening every 3 years for women age 21 to 69 who are, or ever have been, sexually active. Women can stop screening at age 70 if they have had 3 or more normal test results within the previous 10 years .
- Changes in the cervix that lead to cancer (called precursor or pre-cancerous lesions) usually develop slowly over many years. Screening is the best way to find the early cell changes that might lead to cervical cancer because early cell changes do not have any symptoms.
- Colposcopy is an exam done by a specially trained doctor (i.e., a colposcopist) after a woman has an abnormal screening test result. This exam is the next step in the investigation of most abnormal screening test results. The colposcopist may remove or take a biopsy of abnormal-looking tissues, make a diagnosis and, if necessary, develop a treatment plan. After the diagnostic process is complete, a woman with a precursor lesion requiring treatment may undergo a loop electrical excision procedure, laser therapy or cold knife cone biopsy . Treating precursor lesions can prevent cervical cancer from developing.
What is positive predictive value?
- PPV is a quality measure that assesses the likelihood that someone with an abnormal screening test result has a pre-invasive cervical cancer (i.e., changes to the cells of the cervix that may develop into cancer). It is influenced by the proportion of abnormal screening test results and the prevalence (i.e., all people alive who currently have a specific disease) of pre-invasive cervical cancer in screen-eligible women.
- PPV varies with age and grade of cervical cancer (low-grade versus high-grade cervical cancer).
What do the results show?
The positive predictive value of the Pap test for pre-cancerous lesions has varied over the years (Figure 1).
- The PPV of the Pap test in Ontario increased from 4.7% in 2012 to 6.7% in 2014. However, there was a slight decrease in 2015, with the PPV dropping to 5.1%.
- The PPV for invasive cervical cancer was consistent across the Local Health Integration Networks (LHINs) (data not shown). It is important to note that the Pap test is not designed to detect invasive cervical cancer. Rather, it is meant to detect pre-invasive abnormalities that may develop into cervical cancer if not treated.
The positive predictive value of the Pap test varies by age of the women screened (Figure 2).
- In 2015, the PPV of the Pap test for pre-invasive abnormalities was highest among women age 30 to 39 (7.0%) and lowest among women age 50 to 69 (2.8%).
Why is this important to Ontarians?
- Most cervical cancers are found in women who have never been screened or those who have been screened less often than recommended by current cervical screening guidance . Organized cervical screening significantly reduces cervical cancer incidence (i.e., new cancer cases) and mortality (i.e., deaths) [4–6]. Long-term reductions in cervical cancer incidence rates and mortality in Ontario are linked to regular screening with appropriate and timely follow-up.
- It is estimated that 748 Ontario women will be diagnosed with cervical cancer in 2018 . In 2017, roughly 150 women died of the disease . This low incidence and low mortality are a measure of the success of Ontario’s screening system, but they also reflect the need for improvement in prevention and early detection of this essentially preventable disease.
- Human papillomavirus (HPV) infections can cause abnormal cell changes in the cervix and abnormal screening test results. Only abnormal cell changes caused by cancer-causing types of HPV put a woman at risk of getting cervical cancer. While there are over 100 different types of HPV, cervical cancer is mainly caused by the 12 to 15 high-risk types of HPV infection. When a high-risk infection persists (does not go away) for a number of years, it can lead to cervical cancer.
- HPV is passed from one person to another through intimate (i.e., skin-to-skin) sexual contact. HPV infections are common, and up to 80% of sexually active men and women will have an HPV infection in their lifetime. Most HPV infections commonly go away on their own without causing any harm, especially in women under age 30. Factors that determine clearance, as opposed to persistence, of a high-risk HPV infection are not well understood.
- Through regular screening and the appropriate and timely follow-up of abnormal results, it is possible to prevent cervical cancer from developing or to detect it early, when it is easier to treat.
- Cancer Care Ontario’s updated guidance recommends HPV testing as the screening test for cervical cancer. Cancer Care Ontario is working with the Ministry of Health and Long-Term Care to implement HPV testing in Ontario’s organized cervical screening program, the Ontario Cervical Screening Program (OCSP).
- In the interim, the OCSP supports continuing to use the Pap test as the cervical screening test.
- Cancer Care Ontario is developing evidence-based strategies to increase access, align processes, improve practices and enhance the quality of colposcopy services in the province. The OCSP recently released evidence-based clinical guidance for the delivery of colposcopy services in Ontario . Next steps include working with regional partners to encourage implementation of this guidance.