Disproportionate Sociodemographic Effects of Suspended Breast Cancer Screening During the COVID-19 Pandemic

During the first quartile of 2020, breast cancer screening, an outpatient, non-emergent and prevention-based diagnostic service, was suspended throughout Canada to help mitigate the spread of COVID-19, and to divert healthcare resources in managing the developing pandemic. ¹ Quantifying the deleterious effects of the breast cancer screening suspension with an area-based, socio-economic lens may help provincial healthcare systems understand the exacerbated effects of postponed cancer screening, and develop focused outreach efforts, specifically during periods of challenging healthcare resource allocation.

The historical observational cohort study by Bentley et al ² utilized the BC Cancer Breast Screening Database in collating and comparing mammographic screening data in the province from the pre-COVID baseline (April 1, 2017 to March 31, 2020) and COVID periods (April 1, 2020 to March 31, 2021). The study had two main objectives. First, the study aimed to quantify the year-over-year percent reduction in breast screening volumes after 10.5 weeks of suspended mammographic screening between pre-COVID and COVID periods. ² Second, using available postal codes, the study sought to demonstrate disproportionate reductions in breast screening volumes and its association with socio-economic metrics through the Canadian Index of Multiple Deprivation (CIMD). ³

The CIMD defines four dimensions of deprivation: Ethnocultural Composition, characterized by one’s self-identity as a minority, being foreign born or recent immigration; Situational Vulnerability as the stability in housing and education variability within a neighborhood; Economic Dependency describes the proportion of employment or social support as the source of income; and Residential Instability as the fluctuations in occupancy and habitation patterns within neighborhoods. ³

The results from this study were intriguing: between the comparable periods, British Columbia performed approximately 58 000 less breast screening mammograms, which corresponded to approximately a 23% reduction. The most affected groups were patients between the ages of 40 and 49, who experienced a 31.3% reduction, followed by those between 50 and 59 years at 28.1%. Patients who had no prior breast screening were observed to have more than a 40% reduction between baseline and COVID periods. Moreover, patients in smaller communities where the population was less than 10 000 were disproportionately affected, where a 27% reduction in breast screening was observed. Patients in both the Interior and Fraser Health Authorities had the highest reductions of breast screening volumes at 30.1% and 26.4%, respectively. ²

Patients in the lowest quintile of income underwent the highest percent reductions in breast screening volumes at 28.1%. Furthermore, the data tended to show a negative correlation between high income quintiles and percent volume reductions—patients with higher incomes tend to experience less breast screening reductions. Correlations between measures of deprivation and breast cancer screening reductions showed that patients in the highest quintile of each of the four dimensions of CIMD—who were defined as the most deprived—had the highest percentage reduction in screening volumes between comparable periods. ²

The results from population-based study in British Columbia of Bentley et al ² are in line with prior studies analyzing the effects of the pandemic-related suspension on breast cancer screening within Canada and the United States. In Ontario, a retrospective observational study by Walker et al ⁴ demonstrated more than 99% decrease in breast cancer screening in April, May, and June 2020 for average risk patients, slightly recovering to 54% decrease in July, and 23% in December, when compared to data in 2019. ⁴ Breast cancer screening for high risk patients experienced less reduction during the same period and recovered by July 2020, when compared to data in 2019. ⁴ In Alberta, an interrupted-time series study by Heer et al ⁵ covering the periods between January 1, 2018 and December 31, 2020 reported a 33% decrease in new breast cancer diagnoses, among other cancers, due to reduction in preventive diagnostic services available. ⁵ In Manitoba, a similar observational study by Decker et al ⁶ utilizing an interrupted study design between April 2020 to August 2021 observed a 54% decrease between the predicted and expected number of screening mammograms upon resumption of screening in June 2020. This was seen to improve to pre-pandemic levels by December 2020, which was postulated to be due to a more centrally organized screening program, allowing the province to adjust more readily. ⁶ In the United States, a similar retrospective cohort study by Miller et al ⁷ aimed to correlate imputed socioeconomic variables such as income, lack of insurance, and percent of population living below the poverty line with baseline and post-COVID breast cancer screening volumes. Miller et al ⁷ showed that patients from disadvantaged neighborhoods are more vulnerable to missing recommended mammographic screening compared to more affluent neighborhoods.

The study by Bentley et al ² boasts several unique strengths, primarily its large provincial, population-based health database servicing a population of over 5 million. Furthermore, the available population-health based data and postal codes provide an insight to the sociodemographic factors that may prove to affect access to these cancer screening tests, specifically during a pandemic. These results corroborate multiple provincial studies demonstrating the delays to a similar degree due to pandemic-related suspension of breast cancer screening^4-6

Some limitations of the study include reliance on postal codes to determine one’s level of deprivation instead of individual, patient-reported socio-economic data, which at times were reported as missing or incomplete. Robust statistical analyses to determine differences and trends among quintiles might also provide better characterization of the sociodemographic groups aside from those in the highest and lowest quintiles. Additionally, studies assessing individuals who experienced delayed care or missed cancer diagnoses during this period may further help drive the importance of breast cancer screening.

Overall, although socio-economic factors already affect access to preventive cancer screening at baseline, Bentley et al ² demonstrates the exacerbated and disproportional effects on specific populations during periods of health care system challenges such as a pandemic. As the understanding of the effects of the COVID-19 pandemic continues to grow, implementing targeted measures in mitigating inequitable access to important screening tests, especially for the most deprived sectors of society, may be of prime consideration.