PREDICTION OF RESPONSE TO ENDOCRINE THERAPY IN BREAST-CANCER USING IMMUNOCYTOCHEMICAL ASSAYS FOR PS2, ESTROGEN-RECEPTOR AND PROGESTERONE-RECEPTOR

Histological sections obtained from 70 patients with breast cancer, al l of whom had received endocrine therapy for metastatic or locally adv anced disease, were assessed for specific immunocytochemical staining of oestrogen receptor and the oestrogen-induced protein pS2. There was also sufficient material from 25 patients for an assessment of proges terone receptor by immunocytochemistry. We found that, when using a '' cut-off'' point of 50% for ER and PR, and of 25% for pS2, ER was posit ive in 22/29 responders and in 12/41 non-responders, and thus was sign ificantly associated with response to endocrine therapy. Similarly, in those subjects in whom PR was measured, PR was positive in 5/14 respo nders and negative in all 11 non-responders, again being significantly correlated with response. However, pS2 did not relate to response, be ing only positive in 10/29 responders and negative in 26/41 non-respon ders. The different response categories varied in their ''percentage o f positivity'' as determined by the 2 tests. Thus, for ER and pS2 we o bserved: complete response 71% for ER compared with 14% for pS2; parti al response-77% compared with 41%; stable disease-36% compared with 64 %; and progressive disease 27% compared with 27%. We conclude that at the present time ER appears to be the most reliable indicator for pred icting response to endocrine therapy in patients with breast cancer. ( C) 1993 Wiley-Liss, Inc.