PAX 2: A Novel Mullerian Marker for Serous Papillary Carcinomas to Differentiate From Micropapillary Breast Carcinoma

Ovarian serous papillary carcinoma. although rarely metastasizing to the breast, is often challenging based on morphology alone, particularly from the micropapillary variant of breast carcinoma Gloss cystic disease fluid protein-15, although a specific marker, cats be negative in up to 50% of breast carcinomas Wilm's tumor gene 1 (WT-1) has been identified its a useful marker to differentiate metastatic ovarian serous papillary carcinoma from primary breast carcinoma. however. it has recently been shown in the micropapillary variant of the primary breast carcinoma making it a less specific marker. PAX 2, a nuclear transcription factor, was recently observed in ovarian serous papillary carcinomas In this study of 89 breast. carcinoma cases, 26 micropapillary carcinoma, and 63 nonmicropapillary carcinoma types were retrieved from our pathology archive, represented on a single tissue microarray (TMA) with a 3-fold redundancy (TMA-1, TMA-2). In addition, whole tissue sections of a variety of benign and neoplastic mullerian tissues were surveyed with the PAX 2 immunostain. All cases were stained with rabbit polyclonal PAX 2 antibody and, in addition, the 5 metastatic ovarian serous carcinoma cases were stained with WT-1 its well for comparison. Only nuclear staining was considered positive. All primary breast carcinomas represented on TMA-1 and TMA-2 were entirely negative for PAX 2 100% (89 89), whereas 100% (5/5) of all metastatic ovarian serous carcinomas showed moderate-to-strong staining PAX 2 expression wits comparable with WT-1 as well ill the metastatic ovarian serous carcinoma group. We therefore conclude that PAX 2 is a promising new, sensitive, and specific mullerian immunomarker for ovarian serous carcinomas (primary and metastatic).