TRPS1 Expression in Breast Carcinomas: Focusing on Metaplastic Breast Carcinomas

TRPS1 has been recently demonstrated as a highly sensitive and specific marker for breast carcinomas. To further explore TRPS1's utility in breast carcinoma, we systematically evaluated TRPS1 expression on tissue microarrays from 160 estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-positive, 94 ER-/HER2+, 117 triple-negative breast carcinomas, and 618 other primary carcinomas (cholangiocarcinoma, endometrial, colorectal, and hepatocellular carcinomas), and whole tissue sections from 64 HER2+, 76 triple-negative, and 67 metaplastic breast carcinomas. The results showed TRPS1 was highly expressed in breast carcinomas (100% of HER2+ and 97.4% of triple negative on whole tissue sections), but almost completely negative in other tested tumor types. TRPS1 was also highly expressed in metaplastic carcinoma (91%), significantly higher than GATA3 (55.2%). The different expression between TRPS1 and GATA3 was most prominent in chondroid/mesenchymal subtypes (100% vs. 36.4%), followed by spindle cell carcinoma (66.7% vs. 44.4%). In addition, TRPS1 was expressed in normal breast ductal epithelial cells with less staining than in carcinoma cells, and TRPS1 showed aberrant membranous staining in HER2+ breast carcinomas that suggests a potential cross-reactivity with HER2 protein.