TRPS1 expression in non-melanocytic cutaneous neoplasms: an immunohistochemical analysis of 200 cases

Background: Although trichorhinophalangeal syndrome type 1 (TRPS1) was initially thought to be highly sensitive and specific for carcinomas and mesenchymal tumors of mammary origin, more recent data suggest its expression is not limited to breast neoplasms but also can be seen in other cutaneous neoplasms, such as extramammary Paget disease and squamous cell carcinoma (SCC) in situ. Methods: Two-hundred cases of non-melanocytic cutaneous neoplasm, including basal cell carcinomas (BCCs) (n =41), SCCs (n =35), Merkel cell carcinomas (MCCs) (n = 25), and adnexal neoplasms (n = 99), were tested for TRPS1 expression using a monoclonal antiTRPS1 rabbit anti-human antibody. Results: TRPS1 expression was present in almost all cases of SCC (94%), with a median H-score of 200, while it was either absent or only focally present in most BCCs (90%), with a median H-score of 5. The difference between BCCs and SCCs in H-score was significant (p<.001). All MCCs (100%) lacked TRPS1 expression. TRPS1 expression was frequently seen in most adnexal neoplasms, benign and malignant, in variable intensity and proportion but was consistently absent in apocrine carcinomas. All endocrine mucin-producing sweat gland carcinomas (EMPSGCs) (100%, 6/6) showed diffuse and strong TRPS1 immunoreactivity, with a median H-score of 300, which was significantly different (p <.001) than that of BCCs. Conclusions: Our study shows that TRPS1 may be an effective discriminatory marker for BCCs and SCCs. It also has a role in distinguishing BCCs from EMPSGCs.