[Immunohistochemical detection of pS2 protein in paraffin sections of breast carcinoma tissue. Comparison with results of an immunoradiometry assay]

The synthesis of pS2 protein is induced through estrogen-dependent transcription of the pS2 gene. The presence of the pS2 protein in breast cancer is thought to be as valuable as receptor status, or even more so, in predicting the response to hormonal therapy. Furthermore, pS2 appears to be a prognostic factor for primary breast cancer. In 162 cases of primary breast cancer, pS2 was tested by immunohistochemical procedures on formalin-fixed and paraffin-embedded tissues. Staining was evaluated semi-quantitatively using an immunoreactive score (IRS). The concentrations of pS2 in tumor cytosol were determined using an immunoradiometric assay. Positive staining for pS2 (IRSor = 2) was seen in 27% of the tumors. Comparison of immunohistochemical and biochemical detection (26% of tumors had pS2 cytosol concentrations above the cut-off value of 26 ng/mg cell protein) revealed an 81% concordance rate (r = 0.76; P0.0001). Univariate analysis showed no significant correlation of immunohistochemical pS2 detection and age or menopausal status of patients, tumor size, tumor grade or nodal status. However, the immunohistochemical pS2 status correlated significantly with the immunohistochemical detection of the estrogen (ER; P0.001) and progesterone receptor status (PR; P0.0001). pS2-positive tumors were ER-positive in 66% of cases and PR-positive in 73%; 89% of pS2-positive tumors were positive for ER and/or PR. The incidence of immunohistochemical pS2 detection was 41% in the group of steroid receptor positive carcinomas (ER- and/or PR-positive) in contrast to 7% in steroid receptor negative tumors (ER- and PR-negative).