Three predominant prostatic proteins

Prostatic acid phosphatase (PAP), prostate-specific antigen (PSA; or gamma-seminoprotein), and beta-microseminoprotein (beta-MSP; PSP94 or beta-inhibin) are the three predominant proteins secreted by the normal human prostate gland. In the epithelium of normal and hyperplastic prostatic acini and ducts PAP, PSA and beta-MSP have an identical immunohistochemical localization. Highly differentiated (grade I) carcinomas contain an almost equal number of PAP-, PSA- and beta-MSP-immunoreactive cells; the incidence of these cells is lower and they display a greater staining variability in the moderately and poorly (grade II-III) differentiated tumours. Especially in poorly differentiated tumours PSA seems to be a more sensitive immunohistochemical marker than PAP or prostatic carcinomas. Moreover, the use of PAP as a marker for prostatic carcinomas is complicated by the reported structural similarities between the prostatic secreted acid phosphatase and lysosomal acid phosphatase occurring in all tissues. The use of beta-MSP as a marker for prostatic carcinomas may be limited by indications of non-prostatic production of this protein.