Study protocol to assess clinical outcomes of breast cancer and its relationship with access to healthcare in Brazil-BREAST trial (BRaziLian outcomE for metAStatic breasT cancer): a prospective observational study in HER2-negative/hormone receptor-positive metastatic disease.

introductionBreast cancer survival rates in low-income and middle-income countries significantly differ from those in high-income countries, indicating limited access to first-line systemic therapy for advanced and metastatic tumours. Recent studies have demonstrated the benefits of combining cyclin-dependent kinase 4 and 6 inhibitors (CDK 4/6) with endocrine therapy in hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced or metastatic breast cancer. However, in Brazil, the population faces limited access to these drugs, particularly in the public healthcare system. METHODS AND ANALYSIS: This prospective observational study will enrol 300 female patients from 20 cancer centres across Brazil, divided into two groups based on healthcare coverage: those treated in the public healthcare system (group 1) and those treated in the private healthcare system (group 2). The use or non-use of CDK 4/6 inhibitors is not dictated by the study protocol but rather reflects real-world treatment decisions made by attending physicians. Patients will be followed for 24 months, stratified according to CDK 4/6 inhibitor usage. The project aims to assess health inequities by evaluating the prognosis of patients treated in the public versus private healthcare systems. Outcomes include progression-free survival (PFS), overall survival (OS), quality of life and cost-effectiveness. Kaplan-Meier curves will be used to analyse PFS and OS, while the Cox proportional hazards frailty model will be employed to compare outcomes between healthcare systems, adjusting for prognostic variables. ETHICS AND DISSEMINATION: The study protocol was approved by the Ethics Committee of the HCor Research Institute (Hospital do Coração/Associação Beneficente Síria), which served as the central ethics board for the trial (study number: CAAE 42538621.5.1001.0060; approval letter number: 4.571.507; date: 3 March 2021). All participating centres also obtained approval from their respective local ethics committees prior to patient enrolment: Ethics Committee of Hospital de Câncer de Barretos-Fundação Pio XII; Ethics Committee of Universidade Estadual de Campinas-UNICAMP; Ethics Committee of Faculdade de Minas Muriaé-FAMINAS; Ethics Committee of Hospital Santa Paula-SP; Ethics Committee of Hospital Alemão Oswaldo Cruz-SP; Ethics Committee of Hospital Regional do Câncer de Presidente Prudente-HRCPP; Ethics Committee of Instituto Brasileiro de Controle do Câncer-IBCC/Oncologia Clínica-SP; Ethics Committee of Instituto de Medicina Integral Prof. Fernando Figueira-IMIP/PE; Ethics Committee of Hospital São Rafael; Ethics Committee of Universidade Federal de São Paulo-UNIFESP; Ethics Committee of Hospital Geral de Fortaleza-HGF; Ethics Committee of Casa de Saúde Santa Marcelina; Ethics Committee of Centro Universitário FMABC; Ethics Committee of Liga Norte Riograndense Contra o Câncer; Ethics Committee of Hospital Mãe de Deus/Associação Educadora São Carlos-AESC; and Ethics Committee of Instituto do Câncer Brasil-ICB. All patients will provide written informed consent. Study findings will be disseminated through scientific publications and presented to a broad range of stakeholders, including patients, physicians, the general public and policymakers. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov identifier: NCT05559528-BRaziLian outcomE for metAStatic breasT cancer (BREAST).