Breast Cancer Registry Platform

EBC cohort: * Female and male patients with early breast cancer (stage I-III defined as breast cancer that has not spread beyond the breast or the axillary lymph nodes) * Patients at the start of their initial systemic treatment for EBC, i.e. at start of neoadjuvant treatment for patients receiving neoadjuvant therapy or at start of adjuvant treatment if no neoadjuvant therapy is given. Treatment can be cytotoxic, endocrine, or targeted substances, whatever was given first ABC cohort I (prospective): * Female and male patients with advanced breast cancer (stage IV defined as synchrone or metachrone diagnosis of distant metastases at inclusion) * Patients at the start of their initial first-line systemic treatment for ABC, which can be cytotoxic, endocrine or targeting a specific signaling pathway, whatever is given first ABC cohort II (retrospective): * Confirmed diagnosis of HR-positive, HER2-negative ABC (stage IV defined as synchrone or metachrone diagnosis of distant metastases at inclusion) * Start of initial first-line systemic treatment for ABC, which can be cytotoxic, endocrine or targeting a specific signaling pathway, whatever is given first, between September 2021 and December 2025 * Inclusion is possible regardless of whether patients are alive or deceased at the time of documentation; for patients alive: written informed consent Prospective cohorts: * Written informed consent * Patients participating in the PRO module: signing of informed consent form and completion of baseline questionnaire before start of initial systemic treatment for EBC or systemic first-line treatment for ABC * All patients not participating in the PRO module: within six weeks after start of initial systemic treatment for EBC or systemic first-line treatment for ABC All cohorts: • Age ≥ 18 years