Trends in breast cancer incidence by estrogen receptor status in the <scp>United States</scp> , 2004–2020

Divergent trends of breast cancer incidence by subtype have been reported in the United States and elsewhere; however, it remains unknown whether this trend has continued until the era of the COVID-19 pandemic. Using high-quality population-based cancer registry data, representing 83% of the US population, this study examined breast cancer incidence rates by estrogen receptor (ER) status in women aged 20-84 years from 2004 to 2020. The incidence rate of ER-positive cancer increased by 1.75% per year from 2004 to 2009 (95% confidence interval [CI] = 1.26%-3.15%) and has slowed to a 0.87% annual increase (95% CI = 0.41%-1.03%) from 2009 to 2019, followed by a 10.2% reduction from 2019 to 2020. Trends were generally similar across race and ethnicity, although young women (20-49 years), Asian or Pacific Islander, and Hispanic women experienced steady increases until 2019. The incidence rate of ER-negative cancer decreased by 3.13% annually (95% CI = -4.2% to -2.55%) from 2004 to 2012, and the decrease stabilized from 2012 to 2019 (annual percent change: 0.55%; 95% CI = -1.30% to 0.92%), followed by a 6.0% reduction from 2019 to 2020, with trends generally consistent by age and across racial and ethnic groups. The stabilization of the steep decline in ER-negative cancer suggests a departure from the encouraging trajectories projected in earlier studies. Coupled with the deceleration in the rise of ER-positive cancer, the latest trend signals a potential stabilization in the previous rise of the proportional burden of ER-positive cancer. Understanding the impact of the pandemic on each subtype of breast cancer individually may provide a more comprehensive insight into its long-term sequelae on survival and mortality.