Breast Cancer Screening Quality and Efficiency
Measure: PPV: percentage of women, age 50 to 74, with an abnormal OBSP screening mammogram result and were diagnosed with breast cancer (ductal carcinoma in situ or invasive) after diagnostic work-up
As of this Report:
In 2016, the positive predictive value (PPV) of breast cancer screening was 6.5% in the Ontario Breast Screening Program (OBSP), Ontario’s province-wide organized cancer screening program. A PPV of 6.5% means that 3,452 of the 53,146 women age 50 to 74 who had an abnormal OBSP screening mammogram were diagnosed with breast cancer. The PPV for mammograms in Ontario has remained steady at around 6% since 2013.
Approximately 25,000 Ontario women age 50 to 72 who were screened through the OBSP in 2014 and received a 2-year screening recall recommendation had a subsequent program mammogram within 18 months (i.e., they had one too soon). This is an indicator of screening participation behaviour that falls outside recommended guidelines. Early return among women who had an OBSP mammogram with a 2-year recall recommendation increased from 4.4% in 2012 to 6% in 2015. Considerable regional variation was present for this indicator.
In 2016, approximately 7,000 women age 30 to 69 who were referred to the High Risk OBSP completed a genetic assessment (through counselling and/or testing) to determine whether they were at high risk for getting breast cancer. Of the women who completed an assessment, approximately 2,000 (nearly one-third) were determined to be at high risk for getting breast cancer, a rate that has remained steady since 2013. The proportion of women at high risk for breast cancer who were subsequently screened in the OBSP with magnetic resonance imaging (MRI) or ultrasound within 90 days of confirmation of their high risk status decreased from 61% in 2013 to 44% in 2016.
What is breast cancer screening?
- Cancer screening is for 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 screening programs for 3 types of cancer: breast, cervical and colorectal.
Measure: Early return: percentage of Ontario women, age 50 to 72, who were screened through the OBSP with a biennial (every 2 years) screening recall recommendation and had a subsequent program mammogram within 18 months of the previous mammogram
As of this Report:
- The purpose of breast cancer screening is to find cancer at an early stage, when it may be smaller and easier to treat.
- A mammogram uses low-dose X-rays to produce images of the breast . A breast magnetic resonance imaging (MRI) scan uses radio waves and a magnetic field to create cross-sectional images of the breast and an intravenous contrast agent (e.g., dye) is used most of the time . Both tests can find breast cancers when they are small, less likely to have spread and more likely to be treated successfully.
- Breast cancer screening with mammography is recommended every 2 years for most women age 50 to 74 .
- Breast cancer screening with mammography and breast MRI (or screening breast ultrasound if MRI is not medically appropriate) is recommended every year for women ages 30 to 69 identified as being at high risk for breast cancer .
- Most women with an abnormal mammogram result will not have breast cancer . More tests are needed after an abnormal mammogram result to determine whether a cancer is present.
- Diagnostic assessment includes additional radiological or surgical procedures, such as diagnostic mammography, ultrasonography, and core and/or open surgical biopsy.
- In Ontario, breast cancer screening occurs through both OBSP and non-OBSP sites. For a map of locations, visit the Breast screening participation and retention section of this year’s Cancer Screening Quality Index (CSQI).
What is positive predictive value?
- PPV is a quality measure that assesses the accuracy of breast cancer screening in finding breast cancer. It is influenced by the abnormal call rate (i.e., the percentage of women referred for further testing due to an abnormal screening mammogram), cancer detection rates and the underlying incidence (i.e., new cases) of breast cancer.
What do the results show?
The positive predictive value of breast cancer screening in the Ontario Breast Screening Program has remained steady over time, but it varies by age group and among Local Health Integration Networks (Figures 1 and 2).
- The overall PPV of OBSP mammograms in 2016 was 6.5%. Mammogram PPV has remained steady at approximately 6% since 2013.
- In 2016, approximately 3,500 of the over 53,000 Ontario women age 50 to 74 who had an abnormal OBSP screening mammogram result went on to be diagnosed with breast cancer.
- Some variation in mammogram PPV by Local Health Integration Network (LHIN) was present. The LHIN with the highest PPV in 2016 was Champlain (9.5%). The LHIN with the lowest PPV in 2016 was North East (4.8%).
- PPV increased with age. In 2016, the PPV of OBSP mammograms was highest in women age 70 to 74 (12.0%) and lowest in women age 50 to 54 (3.5%). A similar pattern can be seen in previous years. PPV increases with subsequent screens, which is why it is higher in older age groups.
- The PPV of a screening test depends on the underlying prevalence of disease (i.e., all people alive who currently have a specific disease) in the population being screened, which may help to explain the variation observed across LHINs and age groups.
- PPV is reported as a single measure for first and subsequent screens in order to be consistent with Ontario’s cervical and colorectal cancer screening programs. National breast cancer screening guidelines have 2 separate PPV targets: one for first screens (≥5%) and one for subsequent screens (≥6%) [4, 5].
Considerable regional variation exists in early return among Local Health Integration Networks (Figure 3).
- In Ontario, early return in women who had an OBSP mammogram and a 2-year screening recall recommendation increased from 4.4% in 2012 to 6% in 2015.
- Of the approximately 413,000 women age 50 to 72 who were screened through the OBSP in 2015 and given a recommendation to re-screen in 24 months (2 years), almost 25,000 (6%) had a subsequent program mammogram within 18 months.
- The LHINs with the lowest (i.e., better) rate of early return for women with an OBSP mammogram and 2-year recall recommendation in 2015 were South East (2.3%) and North East (2.2%). The LHINs with the highest early return for the same time period were Toronto Central (10.6%) and Central (10.4%).
- Early return has increased in Ontario for every cohort of women with biennial screening recall recommendations since 2012. Early return also increased in every LHIN from 2014 to 2015. The LHIN with the greatest increase was Erie St. Clair (an increase of 2.6 percentage points).
- Early return will continue to provide direction for Cancer Care Ontario in its work with its regional partners to promote adherence to risk-appropriate screening intervals across the province.
Early return for breast cancer screening varies by age group (Figure 4).
- In 2015, the percentage of women with a biennial screening recall recommendation who returned for a subsequent program mammogram within 18 months of a previous mammogram was lowest (5.8%) in women age 70 to 72 and highest (6.2%) in the youngest age group (women age 50 to 54). A similar pattern can be seen in previous years.
Measure: Confirmed high risk for breast cancer: percentage of Ontario women, age 30 to 69, who were referred to the High Risk OBSP and were confirmed to be at high risk for breast cancer by genetic assessment (counselling and/ or testing)
As of this Report:
The proportion of women referred for genetic assessment who are subsequently confirmed to be at high risk varies by region (Figure 5).
- The proportion of women who were referred to the High Risk OBSP and were confirmed to be at high risk after referral remained steady from 2013 to 2016 (between 30% and 34%).
- Some regional variation is present for this indicator. In 2016, the LHIN with the highest percentage of women confirmed to be at high risk for breast cancer after genetic assessment was Mississauga Halton (37%). The LHINs with the lowest percentage of women confirmed to be at high risk for breast cancer after genetic assessment were Erie St. Clair (26%) and Central (25%).
- The High Risk OBSP has set a provincial target of 30% or greater for this indicator, meaning that approximately 1 in 3 women who are referred for genetic assessment should be confirmed to be at high risk for breast cancer .
- Monitoring this indicator allows Cancer Care Ontario to see if the high risk referral criteria are interpreted correctly by primary care providers and to ensure that the criteria appropriately identify women who may be at increased risk for breast cancer.
The proportion of women screened in the High Risk Ontario Breast Screening Program within 90 days of confirmation of their high risk status has decreased since 2013 and varies considerably by region (Figure 6).
Measure: Screened within 90 days of confirmation of high risk status: percentage of Ontario women age 30 to 69 screened through the High Risk OBSP within 90 days of confirmation of high risk status
As of this Report:
- In 2016, 44% of women were screened with MRI or ultrasound within 90 days of confirmation of their high risk status a decrease from 2013, when the rate was 61%.
- The High Risk OBSP has set a provincial target of 90% or greater for this indicator, meaning that about 9 in 10 women should be screened within 90 days of confirmation of their high risk status.
- Considerable regional variation exists for this indicator. In 2016, the LHIN with the highest percentage of women screened within 90 days of confirmation of high risk status was South West (70%). The LHIN with the lowest percentage of women screened within 90 days was Champlain (11%).
- In 2016, the percentage of women screened within 90 days of confirmation of high risk status was similar across all age groups (data not shown).
- The decrease in women screened within the 90-day recommendation may be partly related to increasing MRI wait times. Current wait times are available from the Ministry of Health and Long-Term Care at ontariowaittimes.com.
Why is this important to Ontarians?
Mammography is important for the early detection of breast cancer, but it is not perfect.
- Finding breast cancer early increases the number of treatment options available, and it can lead to better treatment outcomes and survival rates .
- A Canadian study on mammography effectiveness in screening programs found that mammograms are associated with a 21% reduction in breast cancer mortality in average risk women age 50 to 69 (compared to no screening) .
- Women without breast cancer who receive abnormal mammogram results (false-positives) may undergo unnecessary additional imaging and biopsies. The likelihood of a false-positive result is lower for re-screens than for initial screens because previous mammograms can be used for comparison .
- Even with a mammogram, some breast cancers are not found (false-negatives). Dense breast tissue and current use of hormone replacement therapy are associated with an increased risk of breast cancer being missed by screening .
- Women should talk to their healthcare provider for more information about the benefits and limitations of screening with mammography.
Organized screening offers several important benefits to women and their healthcare providers.
- The OBSP and High Risk OBSP provide high-quality screening for most women through the use of mammography, and through mammography and MRI for women at high risk (or screening breast ultrasound if MRI is not medically appropriate).
- Quality assurance is ensured through the accreditation of all OBSP sites by the Mammography Accreditation Program (MAP) of the Canadian Association of Radiologists.
- Communication to women and healthcare providers includes the following:
- Women eligible for screening through the OBSP are sent invitations to get screened, along with information about breast cancer screening and details on how to find an OBSP site.
- After their screening appointment, women with normal screening results receive letters telling them their results are normal.
- Women screened through the OBSP receive letters reminding them when to get screened again.
- OBSP sites follow up on abnormal screening results and send normal and abnormal results to a woman’s healthcare provider.
- Coordination and navigation includes the following:
- High Risk OBSP sites arrange genetic assessment (if appropriate) for women referred to the program.
- High Risk OBSP sites book screening mammography and screening breast MRI (or screening breast ultrasound if MRI is not medically appropriate).
- The OBSP indicates whether a woman should be screened in 1 year or 2 years based on her screening results and risk factors.
- OBSP assessment sites help guide women with abnormal screening results through to diagnosis by coordinating follow-up tests and documenting the results of those tests.
The Ontario Breast Screening Program is continually evaluated and improved to maximize benefits and minimize limitations.
- Women are encouraged to get screened through the OBSP. As an organized screening program, it offers important benefits, such as inviting women to participate in screening, reminding screening participants when it is time for their next screening test, informing participants of normal screening results, tracking participants throughout the screening and diagnosis processes, and measuring program quality and performance.
- A robust quality assurance and performance monitoring framework is in place for the OBSP.
- All OBSP screening sites are accredited by the MAP guidelines of the Canadian Association of Radiologists. The MAP guidelines cover radiologist and medical radiation technologist (MRT) qualifications, equipment, quality control, quality assurance, image quality and radiation dose .
- Feedback on performance, which is then compared to national targets and quality standards, is provided annually to all OBSP and High Risk OBSP screening and assessment sites, as well as to individual radiologists.
- The OBSP’s quality assurance program will continue to provide performance feedback to individual OBSP sites, radiologists and MRTs. It will also work to identify opportunities for improvement (where necessary).
- The OBSP continues to expand, with new screening sites being brought into the program in 2017 and 2018.
- Cancer Care Ontario continues to investigate reasons for early return to the OBSP and to consider strategies for improving adherence to appropriate screening intervals.
- Cancer Care Ontario continues to work with the Ministry of Health and Long-Term Care to identify ways to further support the High Risk OBSP so that Ontario women can continue to benefit from the program.