Immunocytochemical detection of prostate specific antigen expression in human primary and metastatic melanomas

Prostate-specific antigen (PSA), a 33 kD glycoprotein, was initially reported to be a tissue specific protein, detected in the seminal fluid and produced by normal and abnormal epithelial cells of the prostate gland, as well as other tissues in the human body. The expression of PSA has been described to be elevated during benign and neoplastic cell growth in the prostate, and in a number of other human malignancies. The presence and production of PSA in human primary cutaneous malignant melanomas (CMMs) and metastatic malignant melanomas (MMMs) has not been reported prior to the present study. We examined the expression of PSA employing a biotin-streptavidin based, alkaline phosphatase conjugated antigen detection technique in routine, neutral formalin fixed, paraffin-wax embedded, 3-4 microns thick tissue sections of 30 CMMs and 10 MMMs. Human postnatal thymic tissue, among others, was used as a negative tissue control, while normal prostate and prostate carcinomas (PCs) were included in the collection of antigen positive tissues. We observed the presence of PSA in 16/30 CMMs and 6/10 MMMs. The intensity of the staining was moderate (C to B) and localized to between 20% and 30% of the total tumor cell population in both CMMs and MMMs, with cells of similar immunoreactivity being clustered in groups within the tumor microenvironment. This result directly contradicts the previous opinion concerning the prostate epithelium specificity of PSA expression and production. The immunophenotype (IP) heterogeneity of malignant melanoma cells in further substantiated by the pattern of their PSA immunoreactivity. The establishment of the clinical significance of these findings necessitates further in vivo and in vitro research in malignant melanomas. PSA related, novel antineoplastic immunotherapy may also be recommended in the treatment of both CMMs and MMMs.