gms | German Medical Science

Introduction: The COVID-19 pandemic adversely affected health care worldwide. Effects became apparent e.g. in the suspension of screening and the reduced access of patients to medical care. In this study, we assessed the impact of the COVID-19 pandemic on colorectal cancer (CRC) incidence stratified by Union for International Cancer Control (UICC) stage in Bavaria in the pandemic and post-pandemic period.

Methods: The study aimed to model the trend of monthly age-standardised incidence rates (ASIR) (old European standard population) in the pre-pandemic (Jan. 2011 to Feb. 2020) and pandemic (Mar. 2020 to Dec. 2021) periods and to predict ASIR for the post-pandemic period (Jan. 2022 to Dec. 2022). We applied an interrupted time-series analysis using a generalized additive mixed model (GAMM), adjusted stepwise for seasonality (monthly variations) and stratified by UICC stage. We measured the gap in CRC incidence by comparing the sum of estimated monthly ASIR by pre-pandemic model for the pandemic period to the observed ASIR during the pandemic period.

Results: Data of 55,643 incident malignant cases of CRC in Bavaria during Jan. 2011 to Dec. 2021 were identified from the Bavarian Cancer Registry database. Gradually decreasing ASIR were observed for CRC in the decade preceding the pandemic, followed by a sudden drop in March 2020, when the first lockdown was enacted. Comparing ASIR of the pandemic period to the estimated ones by the model of pre-pandemic period for the pandemic period showed a significant relative change of -11.6% [95%CI -15.8%; -7.1%]. In 2022, the predicted relative change decreased to -8.1% [95%CI -13.9%; -2.4%]. Stratified by UICC stage, we observed a prominent incidence gap emerging during the pandemic for early-stage CRC (relative change for UICC I: -22.3% [95% CI -27.8%; -15.8%] and for UICC II: -13.0% [95%CI -19.5%; -5.4%]). In 2022, the reduction slightly decreased for UICC I (relative change for UICC I: -19.1% [95%CI -27.6%; -10.6%] and halved for UICC II: -6.5% [95%CI -16.6%; 3.7%]). Reductions were less pronounced for advanced stages during the pandemic period. Compared to the pre-pandemic model, there was a reduction for UICC III CRC during the pandemic (relative change: -12.9% [95%CI

-18.2%; -6.8%]), decreasing slightly in 2022 (relative change: -9.4% [95%CI -15.8%; 0.0%]). Having declined during the first lockdown, UICC IV ASIR briefly increased, but continuously decreased afterwards. Comparing pre-pandemic and pandemic model, we found an incidence gap during the pandemic (relative change: -7.5% [95%CI -14.6%; 0.9%]), which further persisted in 2022 (relative change: -11.3% [95%CI -21.7%; -0.9%]). Average monthly ASIR for unknown stage increased by 14.8% from 0.62 [95%CI 0.48; 0.78] per 100,000 in the pre-pandemic to 0.71 [95%CI 0.56; 0.89] in the pandemic period.

Conclusion: For CRC, ASIR experienced a substantial decline during the pandemic, especially during lockdown periods. Comparing pandemic to pre-pandemic period revealed a significant incidence gap during the pandemic, being more pronounced for UICC I. With the ending of the pandemic situation, the incidence gap diminished but still persisted. Estimating the trend for CRC incidence for the near future, there is no indication for a complete catch-up effect.

The authors declare that they have no competing interests.

The authors declare that an ethics committee vote is not required.