Our meta-analysis showed that increased Slug protein expression in breast cancer was associated with poorer OS (combined HR = 2.21; 95% CI = 1.47–3.33; P < 0.001) and DFS (combined HR = 2.03; 95% CI = 1.26–3.28; P = 0.004). The gene discussed is SNAI2; the disease is breast carcinoma.