RESUMEN
INTRODUCTION: Chile is committed to actively involving patients in their healthcare. However, little is known about how this is translated into clinical encounters. Breast cancer (BC) is the first cause of cancer-related death in Chilean women. National policy guarantees standard care, and treatment decisions should be made along this process that can have long-term consequences for women. So, BC is a particularly well-suited case study to understand the complexity of patient participation in decision-making. OBJECTIVE: To identify the factors that affect the active involvement of patients in the BC treatment decision-making process, considering the perspectives and practices of health professionals and women facing the disease. METHOD AND ANALYSIS: We will conduct a mixed-method study through a convergent parallel design in three stages: (1) A qualitative study: non-participant observation of the tumour board (TB) meetings; semi-structured interviews with key informants from TBs; documentary analyses; semi-structured interviews with women facing BC; and non-participant observations of clinical encounters; (2) a cross-sectional study with 445 women facing BC stages I-III from three hospitals in Santiago, Chile. We will measure the level of expected participation, experienced participation, decisional conflict, quality of life (QoL) and satisfaction with healthcare. Descriptive analysis will be performed, and multivariable binary logistic regression models will be adjusted to identify factors associated with high levels of QoL or satisfaction; (3) an integration study will bring together the data through a joint display technique. ETHICS AND DISSEMINATION: The study has been conceived and will be conducted according to international and local agreements for ethical research. Ethical approval has been granted by two Ethics Committees in Chile.The results will be disseminated to scientific and lay audiences (publications in scientific journals and conferences, seminars and a website for plain language dissemination).