Evaluation of TRPS1 Expression in Pleural Effusion Cytology Specimens With Metastatic Breast Carcinoma

Objectives Recent studies have shown that trichorhinophalangeal syndrome type 1 (TRPS1) is a sensitive and specific marker that shows positive staining in breast carcinoma. We conducted this study to evaluate the role of TRPS1 immunohistochemistry (IHC) in differentiating breast primary vs tumors from other primary sites in malignant pleural effusion cytology specimens (MPECSs). Methods We selected 61 MPECS cases with cell block material available to analyze TRPS1 IHC staining. Of these 61 cases, 38 cases were metastatic carcinoma (MC) from a breast primary. We primarily selected MC cases confirmed as breast origin based on GATA binding protein 3 IHC positivity, except in two of the cases. The remaining 23 MPECS cases were from various primary sites, including urothelial (n = 6), Müllerian (n = 6), lung adenocarcinoma (n = 6), malignant melanoma (MM; n = 3), and squamous cell carcinoma (SqCC; n = 2). Results TRPS1 expression was observed in 35 (92%) of 38 MCs of breast origin. The staining intensity was variable, with 18 (47%) cases showing strong nuclear expression. In comparison, no TRPS1 expression was seen in any cases of urothelial carcinoma, MM, and SqCC. However, four of six Müllerian MC cases demonstrated TRPS1 expression. Conclusions TRPS1 is a new marker that can be used in an IHC panel to investigate breast origin in MPECS.