Examining the impact of the COVID-19 pandemic on invasive breast cancer incidence in Ireland: A population-based study

Background: This study aimed to investigate the COVID-19 impact on invasive breast cancer incidence and one-year survival in Ireland. Methods: Anonymised aggregate population data from the National Cancer Registry Ireland were used to examine incidence between 2014 and 2020 and differences in the distribution of clinical characteristics using chi-squared tests. Negative binomial regression examined the association between incidence and year of diagnosis. One-year survival was examined by year of diagnosis using Cox proportional hazards regression modelling. Results: For 2020, the age-standardised incidence rate (ASR, per 100,000 females) was 131.9, compared to 163.9 for 2019. In 2020, the incidence rate significantly declined (IRR = 0.41, 95 % CI = 0.22, 0.75) relative to 2019. Fewer cases presented through organised screening (-62.3 %), while similar or increased numbers presented with symptoms (0.1 %) and via other methods (9.0 %) respectively in 2020, compared to 2019. Significant differences were observed in case distribution by ER status (p = 0.02) and stage (p < 0.01) between 2019 and 2020. One-year survival was similar for cases diagnosed during 2014–2019 and in 2020 (HR = 1.07, 95 % CI = 0.89, 1.27). Conclusions: These findings demonstrate reductions in invasive breast cancer incidence and no difference in one-year survival following the pandemic onset. Additional studies to determine the longer-term COVID-19 impact are needed.