Expression of pS2 protein in breast cancer.

The pS2 protein was first detected in the oestrogen-dependent breast cancer cell line MCF-7. It may have prognostic value for primary breast cancer, and could be used to predict clinical responsiveness to endocrine therapy. In a retrospective study, the concentrations of pS2 protein were determined in 434 cytosol specimens using an immunoradiometric assay. The median values (4, 6 and 3 ng/mg protein) and the third quartiles (27, 26 and 29 ng/mg) in benign breast tumours (n = 17), and in primary (n = 325) and recurrent (n = 37) breast carcinomas were of the same order of magnitude. In primary breast cancer, high pS2 values (> 26 ng/mg) correlated significantly with a positive oestrogen receptor (ER) status and a high grade of tumour differentiation (P = 0.01). As many as 85% of the pS2 positive tumours were ER positive. A marginally significant correlation (P = 0.06) was also found between pS2 status and the quantitative expression of the ER. However, the pS2 values in ER positive endometrial carcinomas (n = 12) as well as in other benign and malignant genital tumours (n = 43) were more than 30 times lower than those measured in breast tumours. The results reveal a close association between pS2 protein and ER status which appears to be limited to breast cancer.