Adherence to guidance for prioritizing higher risk groups for breast cancer screening during the COVID-19 pandemic in the Ontario Breast Screening Program: a descriptive study

Abstract

Background: Breast cancer screening in Ontario, Canada, was deferred during the first wave of the COVID-19 pandemic, and a prioritization framework to resume services according to breast cancer risk was developed. The purpose of this study was to assess the impact of the pandemic within the Ontario Breast Screening Program (OBSP) by comparing total volumes of screening mammographic examinations and volumes of screening mammographic examinations with abnormal results before and during the pandemic, and to assess backlogs on the basis of adherence to the prioritization framework.

Methods: A descriptive study was conducted among women aged 50 to 74 years at average risk and women aged 30 to 69 years at high risk, who participated in the OBSP. Percentage change was calculated by comparing observed monthly volumes of mammographic examinations from March 2020 to March 2021 with 2019 volumes and proportions by risk group. We plotted estimates of backlog volumes of mammographic examinations by risk group, comparing pandemic with prepandemic screening practices. Volumes of mammographic examinations with abnormal results were plotted by risk group.

Results: Volumes of mammographic examinations in the OBSP showed the largest declines in April and May 2020 (> 99% decrease) and returned to prepandemic levels as of March 2021, with an accumulated backlog of 340 876 examinations. As of March 2021, prioritization had reduced the backlog volumes of screens for participants at high risk for breast cancer by 96.5% (186 v. 5469 expected) and annual rescreens for participants at average risk for breast cancer by 13.5% (62 432 v. 72 202 expected); there was a minimal decline for initial screens. Conversely, the backlog increased by 7.6% for biennial rescreens (221 674 v. 206 079 expected). More than half (59.4%) of mammographic examinations with abnormal results were for participants in the higher risk groups.

Interpretation: Prioritizing screening for those at higher risk for breast cancer may increase diagnostic yield and redirect resources to minimize potential long-term harms caused by the pandemic. This further supports the clinical utility of risk-stratified cancer screening.

Figure 1:

Monthly volumes of OBSP screening mammographic examinations (January 2019 to March 2021) with percentage change from 2019 volumes for the period March 2020 to March 2021. OBSP = Ontario Breast Screening Program.

Figure 2:

Estimated monthly backlog volumes of OBSP screening mammographic examinations (March 2020 to March 2021), by risk group. As of March 2021, an estimated backlog of 340 876 screening mammographic examinations had accumulated. After June 2020, the backlog was estimated under 2 scenarios: prepandemic screening practices and pandemic screening practices. OBSP = Ontario Breast Screening Program.

Figure 3:

Volume of OBSP screening mammographic examinations with abnormal results (January 2019 to March 2021), by risk group. OBSP = Ontario Breast Screening Program. The individual numbers in the panels are the values at the beginning and end of the pandemic study period (March 2020 and March 2021) and in a comparison month before the pandemic (March 2019).