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

Background 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. Methods 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. Results 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