PS2 PROTEIN - A MARKER IMPROVING PREDICTION OF RESPONSE TO NEOADJUVANT TAMOXIFEN IN POSTMENOPAUSAL BREAST-CANCER PATIENTS

Tamoxifen as sole initial therapy is gaining importance in the managem ent of post-menopausal breast cancer patients. Age, oestrogen (ER) and progesterone (PR) receptor status are accurately considered to select patients for hormonal treatment. However, additional markers are need ed. By immunohistochemistry (IHC), we studied tumour expression of ER, PR, pS2, c-erbB-2 and glutathione S-transferase pi (GST pi) on initia l core biopsies of 208 post-menopausal patients with a non-metastatic invasive ductal carcinoma, treated by neoadjuvant tamoxifen therapy. A good response to tamoxifen was defined as tumoral regression greater than or equal to 50% (110 patients). Relationship between response and age, tumour size, T, N, histological grade, ER and PR contents evalua ted by radioimmunoassay, ER, PR, pS2, c-erbB-2 and GST pi expression e valuated by IHC were studied. Univariate and multivariate analysis sho wed that tumoral regression was linked only to pS2 (P = 0.004) and ER (P = 0.018) IHC expression. According to the immunohistochemical profi le, three groups could be defined: pS2- and ER-positive rumours, pS2- or ER-positive tumours and pS2- and ER-negative tumours with response rates of 60%, 45% and 8% respectively. Although prospective studies ar e needed to confirm these results, we conclude that pS2 and ER immunoh istochemical status are useful tools for predicting tumour regression with neoadjuvant tamoxifen in post-menopausal breast carcinoma patient s.