Prognostic and clinicopathological value of Slug protein expression in breast cancer: a systematic review and meta-analysis

Background: Many studies have reported the relationship between prognosis and Slug protein expression in breast cancer patients, but the results are discrepant. Therefore, there is a need for meta-analyses with high statistical power to investigate and further explore their relationship.

Methods: We used PubMed, Embase, the Cochrane Library, Scopus, MEDLINE, and the Web of Science to find studies on breast cancer and Slug. Overall survival (OS) and disease-free survival (DFS) were the study's primary endpoints. We pooled hazard ratios (HRs) and odds ratios (ORs) to assess the association between Slug protein expression and prognostic and clinicopathological parameters. This study was performed using STATA version 14.0 for data analysis. (Stata Corporation, TX, USA).

Results: We conducted a literature search by searching six online databases. Ultimately, we obtained eight studies including 1458 patients through strict exclusion criteria. The results showed that increased Slug protein expression resulted in poorer OS (HR = 2.21; 95% CI = 1.47-3.33; P < 0.001) and DFS (HR = 2.03; 95% CI = 1.26-3.28; P = 0.004) in breast cancer patients. In addition, the results suggested that breast cancer patients with increased Slug protein expression had a higher TNM stage (I-II vs III-IV; OR = 0.42; 95% CI = 0.25-0.70; P = 0.001), a greater tendency to have axillary lymph node metastases (N+ vs N0; OR = 2.16; 95% CI = 1.31-3.56; P = 0.003) and were more prone to estrogen receptor deficiency (positive vs negative; OR = 0.67; 95% CI = 0.45-0.99; P = 0.042). However, Slug protein expression was not associated with age, histological grade, tumor size, progesterone receptor status, or human epidermal growth factor receptor 2 status in breast cancer patients.

Conclusion: This meta-analysis showed that elevated Slug protein expression may be related to poor outcomes in patients with breast cancer. Therefore, Slug is not only an indicator of patient survival but may also become a new target for breast cancer therapy.