Test Details: Immunohistochemical testing is carried out on biopsy/resected tissue specimen. This testing helps to identify specific antigens (proteins) within tissue sections utilizing an antigen-specific antibody .Prostate specific antigen (PSA) also known as kallikrein-3 is a single chain glycoprotein and a serine protease synthesized by the epithelium of prostatic gland and secreted into prostatic ducts. It is expressed in Prostatic carcinoma but about 10% of high-grade prostatic carcinomas are negative for PSA. Low levels of PSA expression are reported in tumours other than prostatic carcinoma. Weak expression level of PSA is found in a subset of salivary duct carcinoma, small cell carcinoma and breast carcinoma in addition to endometrioid carcinoma.