TRPS1 is a useful marker in differentiating metastatic breast carcinoma from pancreatic adenocarcinoma in fine-needle aspiration specimens

Abstract Objectives Distinction of metastatic breast carcinoma (BC) to the pancreas from primary pancreatic adenocarcinoma (PAC) is essential but challenging. Breast carcinoma shares similar morphology and exhibits an overlapping immunohistochemistry (IHC) profile with PAC. We investigated the utility of recently reported trichorhinophalangeal syndrome type 1 (TRPS1) IHC in differentiating metastatic BC from PAC in fine-needle aspiration (FNA) specimens. Methods We assessed consecutive patients of PAC (n = 49). Due to limited cases of metastatic BC to the pancreas (n = 3), cases of metastatic BC (n = 23) in various locations, including lymph node, lung, bone, or soft tissue, were included. Immunohistochemistry for TRPS1 was performed by using the cell blocks obtained from FNA. A quantitative score for TRPS1 expression was calculated by multiplying the intensity and the percentage of positive cells. Immunoreactivity scores were assigned as negative, low positive, intermediate positive, or high positive. Results In 49 PAC cases, 47 (95.9%) exhibited negative while 2 (4.1%) exhibited low positive TRPS1 expression. However, TRPS1 expression was high positive in 23 (88.0%) of 26 metastatic BC cases, including 10 (83.3%) of 12 triple-negative BC (TNBC) and 13 (92.9%) of 14 non-TNBC cases. Conclusions Our results suggest that TRPS1 IHC represents a highly accurate and reliable method for differentiating metastatic BC from PAC.