Matched Case Control Analysis of Breast Cancer- Specific Factors Affecting Risk of Developing SARS-CoV-2 Infection

In this retrospective matched case control study, we aim to identify breast cancer-related risk factors associated with developing COVID-19 and describe outcomes of patients with breast cancer diagnosed with COVID-19.

Women with breast cancer treated at the Medical College of Wisconsin and diagnosed with COVID-19 from March through December 2020 served as cases, and those without COVID-19 within the same timeframe served as controls. Univariate and multivariate comparisons were performed.

Twenty-five cases and 77 controls were identified. All cases were fully matched by age, obesity, county, and race. Mean age was 54.6 versus 54.9, body mass index 31.0 versus 31.6, 48% lived in Milwaukee County, and 68% were White. Regarding COVID-19 outcomes, 24.0% (n = 6) of cases were hospitalized, median length of stay was 2 days, 8% (n=2) needed oxygen, 4% (n = 6) were intubated, and 4% (n = 6) died. COVID-19 led to treatment delays in 40% of cases. On univariate analysis, there was no statistically significant difference in hormone receptor status or breast cancer stage. Being on active chemotherapy (OR 5.8, P = 0.043) significantly increased the likelihood of developing COVID-19.

In this matched case control study of patients with breast cancer, active chemotherapy was significantly associated with an increased likelihood of developing COVID-19, with a trend seen for triple negative disease. These findings support continued strict precautions for those on active chemotherapy and warrant further analysis in those with triple negative disease.