Expression of the embryonic stem cell marker SOX2 in breast carcinoma

Aims: Cancer stem cells (CSC) or cancer initiating cells (CIC) are tumor cells capable of initiation and propagation of the malignant disease. More recently, SOX2 was shown to participate in reprogramming of adult somatic cells to a pluripotent stem cell state and was implicated in tumorigenesis in various organs. In this study, expression of SOX2 in primary breast carcinomas is characterized by an integrated and interdisciplinary approach.

Methods: Paraffin embedded tissue of a series of 95 cases of postmenopausal breast carcinomas was analyzed by immunohistochemistry for SOX2 expression. SOX2 amplification status was further assessed by FISH in representative samples. SOX2 protein expression was determined in the corresponding metastatic lymph nodes.

Results: We identified variable expression of SOX2 within different regions of individual breast carcinomas. SOX2 expression was detected in DCIS and different subtypes of invasive breast cancer. Expression did not correlate with tumor grading. However, high SOX2 expression was associated with larger tumor size and positive lymph nodal status. Corresponding metastatic lymph nodes showed higher SOX2 expression and were significantly more often SOX2 positive than primary tumors.

Conclusion: In this report, we show that the embryonic stem cell factor SOX2 is expressed in a variety of early stage postmenopausal breast carcinomas and metastatic lymph nodes. Our data suggest that SOX2 plays an early role in breast carcinogenesis and high expression may promote metastatic potential. Further studies are needed to explore whether SOX2 can predict metastatic potential at an early tumor stage.