Primary adenocarcinoma of the seminal vesicles is an extremely rare neoplasm. Because prompt diagnosis and treatment are associated with improved long-term survival, accurate recognition of this neoplasm is important, particularly when evaluating limited biopsy material. Immunohistochemistry can be used to rule out neoplasms that commonly invade the seminal vesicles, such as prostatic adenocarcinoma. Previous reports have shown that seminal vesicle adenocarcinoma (SVCA) is negative for prostate-specific antigen (PSA) and prostate-specific acid phosphatase (PAP); however, little else is known of its immunophenotype. Consequently, we evaluated the utility of cancer antigen 125 (CA-125) and cytokeratin (CK) subsets 7 and 20 for distinguishing SVCA from other neoplasms that enter the differential diagnosis.Four cases of SVCA—three cases of bladder adenocarcinoma and a rare case of adenocarcinoma arising in a mullerian duct cyst—were immunostained for CA-125, CK7, and CK20. Three of four cases of SVCA were CA-125 positive and CK7 positive. All four cases were CK20 negative. All bladder adenocarcinomas and the mullerian duct cyst adenocarcinoma were CK7 positive and negative for CA-125 and CK20. In addition, CA-125 immunostaining was performed in neoplasms that commonly invade the seminal vesicles, including prostatic adenocarcinoma (n = 40), bladder transitional cell carcinoma (n = 32), and rectal adenocarcinoma (n = 10), and all were negative for this antigen.In conclusion, the present study has shown that the CK7-positive, CK20-negative, CA-125–positive, PSA/PAP-negative immunophenotype of papillary SVCA is unique and can be used in conjunction with histomorphology to distinguish it from other tumors that enter the differential diagnosis, including prostatic adenocarcinoma (CA-125 negative, PSA/PAP positive), bladder transitional cell carcinoma (CK20 positive, CA-125 negative), rectal adenocarcinoma (CA-125 negative, CK7 negative, CK20 positive), bladder adenocarcinoma (CA-125 negative), and adenocarcinoma arising in a mullerian duct cyst (CA-125 negative).
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