Our analysis revealed that patients with SIX1 overexpression had worse overall survival (OS) (HR: 1.28, 95% CI: 1.03–1.58) and shorter relapse-free survival (RFS) (HR: 1.28, 95% CI: 1.05–1.56), and much worse prognosis for luminal breast cancer patients with SIX1 overexpression (OS: HR: 1.64, 95% CI: 1.13–2.39; RFS: HR: 1.43, 95% CI: 1.06–1.93). Here, SIX1 is linked to breast cancer.