The impact of episodic screening interruption: COVID-19 and population-based cancer screening in Canada

Abstract

Background: Population-based cancer screening can reduce cancer burden but was interrupted temporarily due to the COVID-19 pandemic. We estimated the long-term clinical impact of breast and colorectal cancer screening interruptions in Canada using a validated mathematical model.

Methods: We used the OncoSim breast and colorectal cancers microsimulation models to explore scenarios of primary screening stops for 3, 6, and 12 months followed by 6-24-month transition periods of reduced screening volumes. For breast cancer, we estimated changes in cancer incidence over time, additional advanced-stage cases diagnosed, and excess cancer deaths in 2020-2029. For colorectal cancer, we estimated changes in cancer incidence over time, undiagnosed advanced adenomas and colorectal cancers in 2020, and lifetime excess cancer incidence and deaths.

Results: Our simulations projected a surge of cancer cases when screening resumes. For breast cancer screening, a three-month interruption could increase cases diagnosed at advanced stages (310 more) and cancer deaths (110 more) in 2020-2029. A six-month interruption could lead to 670 extra advanced cancers and 250 additional cancer deaths. For colorectal cancers, a six-month suspension of primary screening could increase cancer incidence by 2200 cases with 960 more cancer deaths over the lifetime. Longer interruptions, and reduced volumes when screening resumes, would further increase excess cancer deaths.

Conclusions: Interruptions in cancer screening will lead to additional cancer deaths, additional advanced cancers diagnosed, and a surge in demand for downstream resources when screening resumes. An effective strategy is needed to minimize potential harm to people who missed their screening.

Keywords: COVID-19; colo-rectal cancer screening; interruption of screening; mammography screening.

Figure 1.

(a) Projected number of incident cases in Canada (*invasive cancer and DCIS combined) in 2018–2026 for the no interruption scenario, 3-, 6-, and 12-month interruption scenarios. (b) Projected cumulative excess breast cancer deaths (95% confidence intervals) for 3-, 6-, and 12-month interruptions. (c) Projected cumulative excess breast cancer deaths for 6-month interruption followed by 6-, 12-, and 24-months of 50% reduced capacity transition periods. (d) Projected cumulative excess breast cancer deaths for 12-month interruption followed by 12- and 24-months of 50% reduced capacity transition periods.

Figure 2.

(a) Projected number of incident colorectal cancer cases in Canada in 2018–2026 for the no interruption scenario, 3-, 6-, and 12-month interruption scenarios. (b) Projected cumulative excess colorectal cancer deaths (95% confidence intervals) for 3-, 6-, and 12-month interruptions. (c) Projected cumulative excess colorectal cancer deaths for 6-month interruption followed by 6-, 12-, and 18-months of 50% reduced capacity transition periods. (d) Projected cumulative excess colorectal cancer deaths for 12-month interruption followed by 12- and 24-months of 50% reduced capacity transition periods.

Figure 3.

(a) Impact of interruption to mammography on additional breast cancers diagnosed between 2020 and 2029 at a later stage resulting from a 3-, 6-, and 12-month service interruption in Canada. (b) Lifetime impact of colorectal cancer screening interruptions on additional colorectal cancers, stratified by cancer stages, resulting from a 3-, 6-, and 12-month interruptions.