Background: Short period from diagnosis to breast cancer (BC) treatment initiation remains challenging for the public health system in Brazil, which may have been further affected by the coronavirus disease-2019 (COVID-19) pandemic. This study assessed BC diagnosis-to-treatment intervals (DTi) in Brazil and the possible effects of the COVID-19 outbreak on delays.

Methods: The Painel de Monitoramento de Tratamento Oncológico database was queried to obtain the number of Brazilian patients with a BC confirmed diagnosis and initiating cancer treatment in the pre-COVID-19 (2013–2019) and during the COVID-19 (2020–2021) periods, adopting a 60-day limit as timely treatment. A p-value of <0.05 was considered significant.

Results: A total of 315,951 cases were included (females: 99.3% and males: 0.7%), of which 251,667 and 64,284 records were computed before and during the COVID-19 years, respectively. Most patients failed to perform the first cancer treatment within 60 days (>60: 51.8%). We observed an upward trend in the number of BC treatments provided in the pre-COVID-19 years (r² = 0.9575; p < 0.05), but the volume of treatments exhibited an average reduction of 24.6% yearly during the COVID-19 pandemic. The average DTi in days was 122.4, 122.5 and 122.3 in the total period studied, before and during the COVID-19 outbreak, respectively. The arrival of COVID-19 in Brazil increased the chances of treatment delay (OR = 1.043; p < 0.05) and inverted the proportion of early/advanced stages at BC diagnosis (55.8%/44.2%–48.4%/51.6%).

Conclusion: COVID-19 has imposed changes in BC care in Brazil, reducing the number of treatments provided by the Brazilian public health system, increasing the chances of delayed treatment initiation despite no differences in DTi averages being identified, and raising the proportion of advanced-stage diagnoses.