The diagnostic utility of trichorhinophalangeal syndrome type 1 immunohistochemistry for metastatic breast carcinoma in effusion cytology specimens.

Abstract

Trichorhinophalangeal syndrome type 1 (TRPS1) is a novel immunohistochemical marker with excellent performance in distinguishing breast carcinoma from other cancers in surgical specimens. The aim of this study was to evaluate the diagnostic utility of TRPS1 compared with GATA3 for metastatic breast carcinoma in effusion cytology specimens. In total, 91 cell blocks of malignant effusion specimens, including 47 metastatic breast carcinomas (nine triple-negative breast carcinomas [TNBCs] and 38 non-TNBCs) and 44 nonmammary malignancies, were selected for TRPS1 and GATA3 immunohistochemistry. Modified H scores ≥ 200 were considered positive staining. The positive rate of TRPS1 was similar between TNBC and non-TNBC (77.8% vs 73.3%, p=.802), whereas the positive rate of GATA3 was lower in TNBC than in non-TNBC (66.7% vs 89.5%, p=.087). The positive rate of TRPS1 was significantly higher in breast carcinoma than in urothelial carcinoma (74.5% vs 0%, p<.001), whereas the positive rate of GATA3 showed no difference between these two (85.1% vs 85.7%, p=.956). Notably, diffuse and strong aberrant expression of TRPS1 was observed in one lung adenocarcinoma and one serous adenocarcinoma in this series. The overall sensitivity, specificity, positive predictive value, and negative predictive value of TRPS1 immunohistochemistry for breast carcinoma were 74.5%, 95.5%, 94.6%, and 77.8%, respectively. TRPS1 is a sensitive and specific marker for metastatic breast cancer in serous effusion cell-block specimens. It shows superior sensitivity and specificity compared with GATA3, especially in the TNBC setting and for excluding urothelial carcinoma.