Incidence, treatment patterns, and mortality for patients with breast cancer during the first year of the COVID-19 pandemic: a population-based study.

Purpose: The COVID-19 pandemic created significant disruptions in the diagnosis and treatment of breast cancer (BC). Several public health measures were taken with limited evidence on their potential impact. In this observational study, we sought to compare the incidence of BC, treatment patterns, and mortality during 2020 versus 2018 and 2019.

Methods: Using the Surveillance, Epidemiology, and End Results program, we identified 37,834 patients with ductal carcinoma in situ (DCIS) and 199,594 with invasive BC between 2018 and 2020. We assessed age-adjusted incidence rates of DCIS and invasive BC as cases per 100,000, treatment patterns, and mortality in 2020 versus 2018 and 2019.

Results: From 2019 to 2020, the incidence of female DCIS decreased from 36.4 to 31.0, and the incidence of female invasive BC decreased from 184.2 to 166.6. Among females, the relative reductions in incidence from 2019 to 2020 were 14.8% for DCIS, 12.1% for stage I, 5.8% for stage II, 2.6% for stage III, and 1.9% for stage IV. Comparing 2020 to 2018-2019 in invasive BC, we observed significant changes in treatment patterns with decreased use of surgery or radiation and increased use of chemotherapy. The 12-month mortality rates were 4.49%, 4.37%, and 4.57% for 2018, 2019 and 2020, respectively. In the Cox model, there were no significant differences in mortality between patients diagnosed in 2020 versus 2018 or 2019.

Conclusions: During 2020, the incidence of BC decreased significantly. There were reductions in surgery and radiation use, but not in chemotherapy. Although vaccines were largely unavailable and COVID-19 treatments were in development, we saw no differences in 12-month mortality in 2020 versus prior years. The impact on BC-specific outcomes requires further follow-up.