Shared decision-making (SDM) requires that individuals are correctly and smoothly supported to make decisions. However, in Japan, development of decision aids (DAs) to support implementation of SDM is lagging behind Western countries, and there are few reports focused on breast reconstruction. Thus, it is unclear if SDM using a DA in the context of the unique national character and medical culture in Japan is useful in decision-making for breast reconstruction, including whether or not to undergo reconstruction. The aim of this multicentre collaborative study is to investigate the clinical effectiveness of SDM using a DA for patients with breast cancer considering reconstruction, from the perspectives of decisional conflict and postoperative quality of life.

A multisite trial will be conducted at 12 facilities certified by the Japanese Society of Breast Oncoplastic Surgery. A cluster-randomised controlled trial is planned at centres that have implemented SDM with DAs and those that have not implemented SDM, but use a conventional surgical explanation and informed consent to make decisions about reconstruction methods. The study participants will be female patients aged ≥20 years with newly diagnosed stage 0–III breast cancer who are interested in breast reconstruction. Data collection includes baseline and follow-up patient surveys and medical record review. The effectiveness of the DA at reducing conflict and regret in decision-making (primary outcome) will be evaluated using the decision conflict scale.

This protocol has been approved by the Kyoto University Central Institutional Review Board, and permission for performance of the study has been obtained from the Ethics Review Board at each participating centre. We plan to disseminate the findings through journal publications and national meetings, including a presentation of the research results at the Japanese Society of Breast Oncoplastic Surgery. Our findings will advance the science of medical decision-making and have the potential to reduce socioeconomic health disparities.

UMIN000052161.