The impact of the COVID-19 pandemic on breast cancer screening, treatment, and overall survival

PURPOSE: We examined the association between the COVID-19 pandemic and screening, treatment, and overall survival for individuals diagnosed with breast cancer in Manitoba, Canada. METHODS: We used population-based data and a quasi-experimental study with an interrupted time series analysis to examine the number of screening mammograms, first treatment rates, and 2-year overall survival prior to and after COVID-19 for individuals diagnosed with breast cancer. RESULTS: There was a significant decrease in screening mammograms 2 years after the start of the pandemic (ratio = 0.73%, 95% Confidence Interval (CI) 0.58, 0.89). From April to June 2020, fewer individuals diagnosed with stage I-III breast cancer had surgery (ratio = 0.59, 95% CI 0.33, 1.07). Fewer individuals diagnosed with stage I-III breast cancer had radiotherapy (RT) (ratio = 0.69, 95% CI 0.53, 0.91). RT factions per person-year were lower (ratio = 0.81, 95% CI 0.71, 0.92, April to June 2020 and 0.60, 95% CI 0.56, 0.66, July 2020 to December 2022). The proportion of individuals with stage I-III ER+ /HER2- breast cancer who had hormone therapy (HT) was lower (ratio = 0.55, 95% CI 0.36, 0.84). The proportion of individuals with stage I-III HER2+ breast cancer who had neoadjuvant chemotherapy (ratio = 3.64, 95% CI 1.18, 11.16) or targeted therapy (ratio = 3.34, 95% CI 1.13, 9.84) was higher. The proportion of individuals who had adjuvant chemotherapy (ratio = 0.14, 95% CI 0.04, 0.47, April to June 2020 and ratio = 0.19, 95% CI 0.08, 0.48, January to December 2022), targeted therapy (ratio = 0.14, 95% CI 0.04, 0.45, April to June 2020 and ratio = 0.18, 95% CI 0.07, 0.45 January to December 2022), or HT (ratio = 0.43, 95% CI 0.22, 0.83) was lower. The proportion of individuals with stage I-III triple-negative breast cancer who had neoadjuvant chemotherapy was higher (ratio = 2.92, 95% CI 1.04, 8.17). There was no difference for any treatment for stage IV breast cancers. There was no difference in 2-year overall survival for stage I-III or stage IV breast cancers. CONCLUSION: In Manitoba, Canada, there was a significant decrease in the number of screening mammograms 2 years after the start of the pandemic. Breast cancer treatment changed in accordance with updated guidelines with no impact on 2-year overall survival.