Planned study population consists of approximately 1,000 adult patients with HER2-positive mBC receiving anti-HER2 therapy in about 50 oncological centers (in each center it is expected to recruit about 20 patients) in different regions in order to provide representative study sample. Patients will be included consecutively from the least recent diagnosis (within defined time period).
Planned retrospective follow-up period for 1 patient is a period starting from the date of mBC diagnosis until end study or until patient's death, whichever occurs first. End of study will be at least 12 months after the latest date of mBC diagnosis to ensure all patients have the opportunity to contribute at least 12 months of data.
Only patients who were diagnosed between the 1st July 2021 and 1st July 2022 will be included. Patients should have at least 12 months of follow-up data. In case patient died within the first 12 months of diagnosis, these data from date of mBC diagnosis until patient's death should also be included. It will be multicenter study
