TRPS1 expression in neuroendocrine neoplasms of breast and other organs.

Background: Primary neuroendocrine (NE) neoplasms of the breast are rare. In the absence of in situ carcinoma, metastasis from other organs needs to be ruled out first. TRPS1 is a recently identified marker for breast origin. In the current study, we investigated TRPS1 expression in breast neuroendocrine neoplasms, including well-differentiated neuroendocrine tumour (NET) and poorly differentiated neuroendocrine carcinoma (NEC), and compared its expression with neuroendocrine neoplasms from other organs, such as lung, gastrointestinal tract and pancreas.

Methods and results: A total of 105 cases of NE neoplasms were included in our study cohort, including 56 from breast (39 NETs and 17 NECs), 18 from lung (12 typical and atypical carcinoids, and 6 NECs), 19 from gastrointestinal tract (10 NETs, 3 NECs, 6 NETs metastases to breast) and 12 from pancreas (9 NETs, 3 NECs). TRPS1 exhibited moderate to strong expression in 38 of 39 breast NETs (97.4%). Four of 17 (23.5%) breast NECs showed weak to moderate staining. By contrast, no TRPS1 staining was observed in any of the 18 lung and 12 pancreatic NE neoplasms. Among 19 gastrointestinal NE neoplasms, only 1 NEC displayed scattered low TRPS1 positivity.

Conclusions: Our study demonstrated that TRPS1 is universally expressed in mammary NET, and it is a valuable marker to distinguish primary mammary NET from metastatic NET of other organs, including lung, gastrointestinal tract and pancreas. TRPS1 has limited utility in differentiating mammary NEC from NEC of other organs. Clinical radiographic correlation is paramount in diagnosing primary NEC of the breast.