Although immediate breast reconstruction following mastectomy has become increasingly common, its oncological safety has been debated. We enrolled patients with breast cancer who underwent surgery at Okayama University Hospital between 2007 and 2013. The primary outcome was relapse-free survival (RFS). Secondary outcomes were overall survival and the duration from the surgery to the initiation of adjuvant chemotherapy. We divided into immediate breast reconstruction, mastectomy alone, and breast conservative surgery groups. Outcomes were compared using Cox’s regression analysis. A total of 614 patients were included (reconstruction: 125, mastectomy: 128, breast conservative surgery: 361). The median follow-up duration was 79.0±31.9 months. ...