Abstract Objective. This survey was conducted with medical oncologists treating breast cancer and explores how the COVID-19 pandemic has impacted their approach to managing breast cancer.Method. A questionnaire of ten questions was sent electronically to 123 medical oncologists throughout the Mexican Republic from June 25 to 29, 2020, a critical moment in our patient with the highest reports of new cases of patients with COVID-19.Results. Of the respondents, 47.1% work in a public and private hospital, 21.9% and 30.0% exclusively in the public and private respectively. Modification of treatment schemes due to the pandemic is reported in 42.5% (51) and 34.1% (41) occasionally. The dose modification has occurred mainly in the palliative context 71.3%. The modification of intravenous to oral chemotherapy was confirmed in 78.2% of the respondents, but this was in less than 30% of the patients. Only 27.1% of doctors have prolonged their chemotherapy schedules. To the question of postponing visits in patients under surveillance or in adjuvant with endocrine therapy, 80% of the doctors answered confirmatory. Private online consultation has been implemented in 57.8% of doctors. When asked to have patients with breast cancer and a positive test for COVID-19, 37% (43 doctors) confirmed having had patients. Delays in diagnostic protocols for breast cancer were reported in 74.5% (85). Finally 37.7% reported that less than 25% of their patients did not attend their scheduled appointment and 32.4% of the doctors reported that between 25% to 50% of their patients postponed the medical visit. (See images of results).Conclusion. In Mexico, like many countries, the treatment and follow-up of patients with breast cancer has been affected by the pandemic, a factor that impacts the results is that in our country we have a shortage of oncological drugs for more than a year, including sometimes cyclophosphamide, anthracyclines and taxanes that are essential for this disease. Management and diagnosis protocols have been delayed since medical care has been prioritized for patients with COVID-19. Unfortunately, there is no national registry of cancer patients, much less the association of cancer with COVID-19. The study, however, reflects similarity of results with other countries in medical behavior. Citation Format: Ricardo Villalobos Valencia, Samuel Rivera Rivera. Patterns of medical behavior in the management of breast cancer during COVID-19. Mexican Experienc abstract. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SS2-03.