Real-world Bicohort Observational Study of a Pertuzumab Biosimilar in the Treatment of Breast Cancer: in the Neoadjuvant Setting and in First-line Metastatic Disease

Inclusion Criteria: * Age ≥ 19 years at the time of inclusion; * Histologically confirmed diagnosis of HER2-positive invasive breast cancer (IHC 3+ score or HER2 amplification by FISH/CISH/SISH); * Decision to initiate treatment with a pertuzumab biosimilar in the neoadjuvant setting (neoadjuvant cohort) or as first-line therapy in the metastatic setting (metastatic cohort), in accordance with local indications; * Treatment prescribed as part of routine clinical care (outside of a clinical trial); * Patient informed and having provided written informed consent. Exclusion Criteria: * Treatment with pertuzumab in a therapeutic setting other than neoadjuvant or first-line metastatic (e.g., adjuvant, late recurrence beyond first-line, maintenance therapy alone, etc.); * Treatment administered as part of an interventional clinical trial; * History of severe allergy or known contraindication to pertuzumab; * Medical records unavailable or inability to ensure at least 6 months of minimal follow-up.