Objectives: To examine whether there is a difference in the number of patients with breast cancer before and during the COVID-19 pandemic, and to examine whether there is a difference in the stage of the disease and the size of breast cancer before and during the pandemic. Study Design: Cross-sectional study with historical data Participants and methods: The participants are patients who were diagnosed with breast cancer in the period from 2019 to 2022 at the Clinic for Oncology and Radiotherapy of the Clinical Hospital Center Osijek. Patients with cancer in both breasts were excluded from the study. Results: The study included 876 patients diagnosed with breast cancer. Of the total number of patients, 294 (33.6%) patients were diagnosed before the COVID-19 pandemic, and 582 (66.4%) during the COVID-19 pandemic. There are no significant differences in tumor size regarding the period before and during the COVID-19 pandemic. Most patients, 449 (51.3%) were diagnosed at stage II, while there were a total of 69 (7.9%) patients with stages III and IV. The values of the proliferation index (Ki-67) were significantly lower in patients who were diagnosed before the pandemic compared to the time during the pandemic. HER2 was significantly more present in patients during the pandemic compared to the period before the pandemic. Conclusion: The COVID-19 pandemic did not significantly affect the reduction in the number of diagnosed patients with breast cancer, the incidence of advanced stages of the disease, and the size of breast cancer at the Clinical Hospital Center Osijek.