Advanced prostate cancer with normal serum prostate-specific antigen values.

Prostate-specific antigen is a specific and sensitive marker of prostate cancer, and most patients with advanced prostate cancer have elevated serum prostate-specific antigen values. Over a period of 45 months, 976 cases of advanced prostate cancer (stages C and D) were investigated to determine the serum prostate-specific antigen level at presentation. Eight cases of advanced prostate cancer are documented in which the serum prostate-specific antigen values were within normal limits. Six of the eight cases showed the features of invasive moderately differentiated acinar carcinoma; one case of small-cell carcinoma and one of cribriform carcinoma were noted. Direct immunohistochemical assessment of tumor tissue was performed, and the correlation between monoclonal and polyclonal antibody staining was assessed. In seven of the eight cases, monoclonal antibodies showed no convincing staining, while all but one (small cell) were positive for polyclonal stains.