Association Between High Expression of Phosphorylated-STMN1 and Mesenchymal Marker Expression and Cancer Stemness in Breast Cancer

Background/Aim: In patients with breast cancer, the expression of stathmin1 (STMN1) has been significantly related to a poor prognosis, cancer aggressiveness, and expression of cancer stem cell markers. The STMN1 protein is closely regulated by phosphorylation in four sites. However, few studies have investigated the relationship between the expression of phosphorylated STMN1 (pSTMN1) and clinicopathological findings, including tumor-aggressive biomarkers, in patients with breast cancer. Materials and Methods: The expression levels of four pSTMN1 (Ser16, Ser25, Ser38, and Ser63) were immunohistochemically analyzed in 213 breast cancer cases. The clinicopathological factors evaluated included epithelialmesenchymal transition (EMT) markers and cancer stem cell markers. Results: The cytoplasmic expression of pSTMN1 (Ser16, Ser25, Ser38, and Ser63) in normal breast tissues was low. The positive expression ratios of Ser25 (54.5%) and Ser38 (39.0%) were high compared to those of Ser16 (25.8%) and Ser63 (23.9%). The overexpression of pSTMN1 (Ser38) was associated with tumor-aggressive characteristics, such as triple negative breast cancer (TNBC) phenotypes, high mesenchymal marker, and expression of cancer stem cell markers. Conclusion: STMN1 phosphorylation might be associated with clinicopathological factors, breast cancer subtypes, and expression of mesenchymal markers and breast cancer stem cell markers through the regulation of STMN1 function. Ser38 phosphorylation of STMN1 may be a novel biomarker for highgrade TNBC associated with mesenchymal marker expression and cancer stemness.