Prostate-specific antigen (PSA)
Prostate-specific antigen (PSA) is a single-chain 34-kd glycoprotein
of 237 amino acids containing approximately 8% carbohydrate. It is a
serine protease produced almost exclusively by prostatic epithelial
cells. PSA has chymotrypsin-like, trypsin-like and esterase-like
activity. From the epithelial cells of the prostate, PSA is secreted
via the prostatic ductal system into seminal plasma, where it
catalyses the liquefaction of the seminal coagulum after
ejaculation. The PSA gene, which belongs to the kallikrein gene
family, is located on chromosome 19, region 13q.
readily demonstrated in adenocarcinomas of the prostate in
about 99% of the cases (Figs. 2A-F).
There is a correlation between malignancy grade and intensity of
staining, high grade carcinomas displaying weaker expression
About 1% of poorly differentiated carcinomas have been negative
for PSA. Radiation has not been shown to influence
immunohistochemical PSA detection but reduction of staining
intensity has been described following hormonal treatment.
Different types of prostatic carcinoma, including ductal
adenocarcinoma, mucinous, signet ring and small cell carcinoma,
have been described to express PSA, whereas rare carcinoma with
squamous differentiation as well as adenoid cystic carcinoma have been
negative for PSA.
PSA has been found in rare urethral papillomas (Fig. 2G) and in some extraprostatic neoplasms, such as female and male breast carcinoma, as well as salivary and sweat gland tumours.
Due to the high specificity of PSA for prostatic
glandular epithelium, it is very useful in identifying prostatic
carcinoma in the prostate and in the adjacent organs often affected
by epithelial malignancies, i.e. rectum and urinary bladder (Figs.
adenocarcinoma, urothelial carcinoma or adenocarcinoma of the
urinary bladder no not express PSA. Lack of PSA immunoreactivity in
a very poorly differentiated malignancy does not, however, exclude
the diagnosis of prostate cancer.
mAbs ER-PR8, PSA-001,07, OS94.3, PSB535, 2009 and
SC.5; pAbs (DakoCytomation). Staining of non-prostatic tissue is
more frequently seen with pAbs indication some vross reaction with
Alanen KA, et al.
Immunohistochemical labelling for prostate specific antigen in
non-prostatic tissues. Pathol Res Pract 1996;192:233-237.