Impact of the COVID-19 Pandemic and Lockdown on Cancer Diagnoses Using Swiss Cantonal Cancer Registry Data

<b>Background/Objectives:</b> This study aims to investigate differences in cancer diagnosis based on absolute case numbers and age-standardized incidence rate ratios (IRRs) in the pre-Coronavirus disease 2019 (COVID-19) years (2018/19) and the first two years of the COVID-19 pandemic (2020, 2021) in two Swiss cantons. <b>Methods</b>: Data of the Swiss cantonal cancer registry of the cantons of Zurich (ZH) and Zug (ZG) were used to descriptively investigate differences in annual and monthly absolute numbers regarding all-cancer and the five most common cancer types. Directly age-standardized monthly incidence rates (IRs) were calculated. Multivariate Quasipoisson regression models were fitted to determine the IRRs with 95% confidence intervals (95% CI). <b>Results</b>: Annual absolute numbers of all investigated cancers were similar in 2018/19, 2020, and 2021, except for prostate cancer (increase of 20.8% in 2021 compared to 2018/19). In 2020, there were generally more cancer diagnoses in January and February followed by a decrease in April and May. Compared to the pre-COVID-19 period, lower IRs were observed in 2020 for all-cancer (IRR = 0.96 [95% CI 0.96, 0.97]) and female breast cancer (0.92 [0.89, 0.96]), whereas higher IRs were observed in 2021 for all-cancer (1.02 [1.02, 1.02]) and prostate cancer (1.23 [1.18, 1.28]). <b>Conclusions</b>: Cancer detection and diagnoses decreased during the first year of the pandemic, especially during the most stringent lockdown phase in April. The findings of this study may inform the decisions of policymakers and public health system during future pandemics.