Protein level of epithelial membrane protein (EMP) 1, EMP 2, and EMP 3 in carcinoma of unknown primary.

Carcinoma of unknown primary (CUP) is defined as a metastatic carcinoma whose primary site cannot be determined, and the absence of a known primary tumor in CUP poses a significant challenge in treatment planning. The purpose of this study was to investigate the protein level of epithelial membrane proteins (EMP) 1, EMP 2, and EMP 3 in CUP and explore their clinical implications. Tissue microarrays were constructed using samples from 72 CUP cases. The histologic subtypes were adenocarcinoma (ADC) in 22% of cases, poorly differentiated carcinoma (PDC) in 15%, squamous cell carcinoma (SCC) in 19%, and undifferentiated carcinoma (UDC) in 14%. Clinically, 17 cases (23.6%) were of favorable type, and 55 cases (76.4%) were of unfavorable type. Immunohistochemical staining for EMP 1, EMP 2, and EMP 3 was performed on the tissue microarrays to investigate the correlation between staining results and clinicopathologic parameters. The investigation of EMP 1, EMP 2, and EMP 3 protein levels in CUP revealed that EMP 2 H-score was significantly higher (p=0.013) in the favorable type, and there was a higher proportion of stromal EMP 1-positivity (p=0.034) and high protein level of tumoral EMP 3 (p=0.002). A positive correlation was observed between EMP 1 and EMP 3 (r=0.425 and p<0.001). In conclusion, CUP exhibits EMP 1, EMP 2, and EMP 3 protein levels, and their protein levels are different according to the clinical subtype.