MUC16 and prostate cancer: However, the immunohistochemistry of seminal vesicle carcinoma is characterized by positive staining for cancer antigen 125 (CA-125) and cytokeratin (CK)-7 and a lack of expression of membrane prostate-specific antigen, which helps differentiate the rare diagnosis of seminal vesicle carcinoma from the more frequent cases of prostatic cancer invading the seminal vesicles[4].