Does SOX-2 expression have a prognostic value in triple-negative breast cancer?

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer. At the cell of origin level, cancer stem cells (CSC) are the tumour initiators in breast cancer. SRY-box transcription factor 2 (SOX-2) is a CSC marker that plays a role in tumourigenesis. The objective of this study was to evaluate the association of SOX-2 expression with histopathological parameters and clinical outcomes in TNBC patients. The study included 95 TNBC cases. An in vitro diagnostic SOX-2 antibody was applied to the tumoural slides in a validated automated stainer. The expression of SOX-2 was defined as a SOX-2 H-score ≥ 1. The expression of SOX-2 was observed in 29 cases (30.5%). At a median follow-up of 76 months, SOX-2 expression was not associated with overall or disease-free survival. R-based statistical analysis determined a SOX-2 H-score cut-off of 2. Although the overall and disease-free survival rates of cases with an H-score ≥ 3 were lower than the others, the differences were not statistically significant. The percentage of SOX-2 staining is typically low, as only 1% of tumour cells exhibit CSC characteristics. In conclusion, the prognostic significance of SOX-2 could become clear in a larger group of TNBC patients using standardized methodologies.