Characterization of paired box 8 (PAX8)-expressing metastatic breast carcinoma

Background/Aim: Paired box 8 (PAX8) is an organ-specific marker discriminating Müllerian and breast carcinomas. Recent studies have described PAX8 expression in a small subset of breast carcinomas, which may cause a diagnostic pitfall in the determination of cancer origin. The aim of this study was to investigate characteristics of PAX8-expressing metastatic breast carcinomas (MBCs) to help elucidate the primary site of occurrence. Patients and Methods: Using immunohistochemistry, we examined PAX8 status in 80 MBCs and 52 matched primary breast carcinomas (PBCs). Results: A total of 20% of MBCs displayed PAX8 expression and the concordance rate of PAX8 expression between MBCs and PBCs was 92.3%. In MBCs, PAX8 expression was significantly associated with high-grade features (p=0.042), estrogen and progesterone receptor negativities (p=0.005 and p=0.017, respectively). Conclusion: PAX8 may be identified in MBCs with high-grade and non-luminal molecular subtypes. Careful assessment is needed when designating a primary site relying principally on PAX8 positivity.