Interpreting Cancer Incidence Trends: Challenges due to the COVID-19 Pandemic.

The significant deficit in cancer diagnoses in 2020 due to COVID-19 pandemic disruptions in health care, can pose challenges in the estimation and interpretation of long-term cancer trends. Using SEER (2000-2020) data, we demonstrate that inclusion of the 2020 incidence rates in joinpoint models to estimate trends can result in a poorer fit to the data, less accurate, or less precise trend estimates, providing challenges in the interpretation of the estimates as a cancer control measure. To measure the decline in 2020 relative to 2019 cancer incidence rates, we use the percent change of rates in 2020 compared to 2019. Overall, SEER cancer incidence rates dropped approximately 10% in 2020, but for thyroid cancer the drop was as big as 18%, after adjusting for reporting delay. The 2020 SEER incidence data is available in all SEER released products, except for joinpoint estimates of trends and lifetime risk of developing cancer.