Technical variations in prostatic immunohistochemistry: need for standardisation and stringent quality assurance in PSA and PSAP immunostaining.

AIMS: To assess variations in prostate specific antigen (PSA) and prostate specific acid phosphatase (PSAP) immunohistochemistry with particular reference to the antibody type (monoclonal or polyclonal) and the tissues used for optimising immunostaining conditions and as external positive controls.
METHODS: A questionnaire was sent to all laboratories registered with the UK National External Quality Assurance Scheme for immunohistochemistry enquiring about the immunohistochemical methods routinely used for the diagnosis of prostate cancer.
RESULTS: Responses were received from 220 (68%) laboratories. All UK respondents routinely performed PSA immunostaining but PSAP immunostaining was available in only 57% of these laboratories. Monoclonal anti-PSA, polyclonal anti-PSA, monoclonal anti-PSAP, and polyclonal anti-PSAP were used by 40%, 60%, 29%, and 27% of UK respondents, respectively. Benign prostate tissue was most commonly used to determine optimal antibody dilutions and as external quality control for PSA/PSAP, with only 6% and 3% of respondents, respectively, including high grade prostate cancer in the tissues used for these purposes.
CONCLUSIONS: The wide variation in the methods used highlights the need for standardisation and more stringent quality assurance of the immunohistochemical staining techniques used for PSA and PSAP. The widespread use of benign prostate tissue to determine optimal antibody dilutions and as an external positive control for PSA and PSAP immunostaining is of particular concern because this approach may result in a method that is not sufficiently sensitive to detect the reduced PSA and PSAP expression associated with high grade prostate cancer.