Cardiotoxicity and mortality trends in chemotherapy-treated breast cancer patients before and during the COVID-19 pandemic.

e24013 Background: The Coronavirus Disease 2019 (COVID-19) pandemic caused widespread disruptions in breast cancer screening, diagnosis, and treatment delivery, raising concerns about downstream impacts on treatment-related morbidity and mortality. While excess mortality during the pandemic has been documented in the general population, its implications for cancer, particularly those exposed to potentially cardiotoxic chemotherapy remain insufficiently characterized. This study evaluates whether cardiotoxicity and mortality outcomes among breast cancer patients treated during 2019–2022 differed from prior years. Methods: We conducted a retrospective cohort study within Kaiser Permanente Southern California (KPSC), including adults (≥18 years) diagnosed with primary breast cancer from 2007–2022 who received ≥1 cycle of cytotoxic chemotherapy. Cardiotoxicity and mortality outcomes were compared across four periods: 2007–2010, 2011–2014, 2015–2018, and 2019–2022 (reference, representing the COVID-19 period) based on year of chemotherapy initiation. Proportional hazards models adjusted for demographic factors, tumor characteristics, smoking status, and pre-existing cardiovascular disease (CVD) conditions or risk factors. Cardiotoxicity was defined as either congestive heart failure (CHF), cardiomyopathy, or major adverse cardiac/cardiovascular events (MACE). Mortality analyses evaluated all-cause, cancer-specific, and CVD-specific deaths. Results: Among 12,302 chemotherapy-treated patients, cardiotoxicity rates during 2019–2022 were comparable to those in all pre-pandemic periods, with no significant increases in CHF, MACE, or cardiomyopathy. In contrast, mortality outcomes were consistently worse in earlier periods (Table 1). All-cause mortality was elevated in 2007–2010 (HR 1.16, 95% CI 1.00–1.36), and cancer-specific mortality was markedly higher in 2007–2010 (HR 1.97, 1.65–2.35), 2011–2014 (HR 1.56, 1.31–1.87), and 2015–2018 (HR 1.31, 1.09–1.56). CVD-related mortality was also higher in 2007–2010 (HR 1.70, 1.32–2.21) and 2011–2014 (HR 1.41, 1.09–1.83). Conclusions: We observed no increase in chemotherapy-associated cardiotoxicity or cause-specific mortality during the 2019–2022 COVID-19 period compared with earlier years. Cardiotoxicity rates, including CHF, MACE, and cardiomyopathy, remained stable, and all-cause, cancer-specific, and CVD-specific mortality were not elevated. These findings suggest that continuity of oncology and cardio-oncology care can be maintained even during major healthcare disruptions. Hazard ratios for CHF, MACE, cardiomyopathy. Year Quartiles CHF MACE Cardiomyopathy 2007-2010 0.92 (0.71-1.20) 1.09 (0.95-1.23) 1.02 (0.76-1.38) 2011-2014 1.00 (0.78-1.28) 1.04 (0.91-1.20) 0.89 (0.66-1.19) 2015-2018 0.99 (0.78-1.25) 0.96 (0.84 -1.10) 1.09 (0.83-1.45)