Introduction: We are currently living in a state of pandemic by COVID-19, whose virus has high transmissibility and potential lethality. The World Health Organization recommended social isolation, and the Brazilian National Cancer Institute, following this guidance, proposed that the oncological treatment of low-to-moderate aggressive tumors be postponed, including breast cancer. In Brazil, the lockdown was a strategy to reduce the potential impact of the pandemic on health services; consequently, asymptomatic patients postponed their imaging tests this year. Considering this abrupt change in access to health care and in the routine of cancer screening, we theorize that the COVID-19 pandemic may have had a negative impact on diagnosis, treatment, and survival in breast cancer patients. Objective: The aim of this study was to analyze the staging at diagnosis of patients with breast cancer, before and during the pandemic, and to calculate if there was a statistical difference comparing the two groups studied. A secondary objective was to describe clinical and demographic characteristics. Methods: A single-center, cross-sectional analytical study with 1219 patients diagnosed with breast cancer (CID C50 or D05) treated at the Mastology Department of the AC Camargo Cancer Center from March 2019 to February 2021. The following epidemiological variables were evaluated: age at years at diagnosis, clinical staging at diagnosis (TNM 8th edition©), presence of comorbidities (risk group for severe COVID-19), family history of cancer, symptoms at diagnosis, and provenance. Descriptive variables and data analysis was performed using Pearson’s χ2 test or Fisher’s exact test. Results: In this study, 1002 patients were included, divided into two groups: prepandemic (574) and pandemic (428). Both groups had similar demographic and clinical characteristics. There was an increase in the frequency of symptomatic patients in the pandemic period 199 (46.5%) versus nonpandemic period 213 (37.1%) (p=0.003). Anatomical and clinical staging were similar between the groups, with no statistically significant difference. When analyzing the anatomical staging, comparing the prepandemic versus pandemic groups, we observed a higher frequency of tumors: T1 [262 (45.6%) vs. 170 (39.8%), p=0.376]; N0 [398 (69.2%) vs. 288 (67.4%), p=0.194]; M0 [552 (96.0%) vs. 415 (97.2%), p=0.614]. Regarding clinical staging, early malignant tumors (EC Tis, Ia–IIIa) were more frequent, corresponding to 521 (90.8%) prepandemic versus 390 (91.1%) pandemic (p=0.766). Conclusion: There was no significant variation between the groups in terms of staging at diagnosis, but more patients with symptoms related to breast cancer sought cancer care.