The results showed that breast cancer patients with increased Slug protein expression had a higher TNM stage (I–II vs III–IV; pooled OR = 0.42; 95% CI = 0.25–0.70; P = 0.001) (Additional file 3: Figure S1a), were more prone to axillary lymph node metastasis (N+ vs N0; pooled OR = 2.16; 95% CI = 1.31–3.56; P = 0.003) (Additional file 3: Figure S1b) and had more severe ER deficiency (positive vs negative; pooled OR = 0.67; 95% CI = 0.45–0.99; P = 0.042) (Additional file 3: Figure S1c). The gene discussed is SNAI2; the disease is metastatic malignant neoplasm in the lymph nodes.