Access to care disruptions due to the COVID-19 pandemic are the likely cause of the drop in the reported number of cancer cases in 2020, and new research shows that while overall incidence rates in 2021 were closer to prepandemic expectations, later-stage breast cancer numbers were up, indicating the potential impact from the disruption in screenings during the previous year.

The study, published in the Journal of the National Cancer Institute, from the National Cancer Institute, compared observed 2021 cancer incidence rates with expected prepandemic trends for all cancers combined and five specific cancer sites: female breast, prostate, lung and bronchus, pancreas, and thyroid. The analysis also included stage-specific comparisons for these cancers. Researchers analyzed data from 22 cancer registries in the Surveillance, Epidemiology, and End Results (SEER) Program—representing approximately 48% of the US population—finding overall cancer incidence rates returned to prepandemic levels in 2021. However, the data did not exhibit a rebound effect to account for the decline in cancer diagnoses observed in 2020.

Expected prepandemic incidence rates for 2020 and 2021 were projected using the model's parameters from the last segment. Rate ratios comparing observed 2021 rates to expected rates were calculated, along with 95% confidence intervals.

For all cancers combined, the 2021 observed age-adjusted rate was 458.33 per 100,000, while the expected rate was 459.06 per 100,00. The rate of overall incidence of female breast cancer was 137.42 per 100,000, which is near the expected rate of 140.49. However, the observed 2021 rate of distant breast cancer was 8.44 per 100,000, which was higher than the expected rate of 7.76 per 100,000.

Other cancers showed declines in the observed rate when compared with the expected rates. For prostate cancer the overall observed rate of 127.97 per 100,000 while the expected rate was 135.06 per 100,000. A similar drop was observed with lung and bronchus cancer where the overall rate of 46.93 per 100,000 was below the expected rate of 49.40 per 100,000, as well as for pancreatic cancer which showed an observed rate of 13.92 per 100,000 against an expected rate of 14.31 per 100,000, and for thyroid cancer where the observed rate was 13.62 per 100,000 while the expected rate was 14.57 per 100,000.

Researchers employed Joinpoint Trend Analysis Software version 5.1.0 to estimate prepandemic trends by cancer site and stage. The analysis fitted Joinpoint models to 2000-2019 incidence rates for overall trends and 2004-2019 rates for stage-specific trends. The models allowed a maximum of 3 joinpoints for overall trends and 2 joinpoints for stage-specific trends.

The study analyzed data from 2000 to 2021 for overall cancer trends, with stage-specific analysis covering the period from 2004 to 2021. The authors defined a rebound as a statistically significant increase in rates in 2021 compared with what would have been expected or estimated in the absence of the COVID-19 pandemic.

Limitations of the study included the assumption that prepandemic trends would have continued in the absence of the pandemic, potential uncertainties in extrapolating trends beyond the observed data range, and caution in interpreting projected trends when a joinpoint occurs toward the end of the data series.

The authors note that further monitoring and research is needed to understand and address the full impact of the COVID-19 pandemic on cancer screenings and patient outcomes.

The authors declared no potential conflicts of interest.