Value of immunohistochemical-determined oestrogen receptor status and proliferative activity in breast cancer: A retrospective study including patients treated by endocrine therapy at the time of recurrence

The oestrogen receptor (ER) status and the proliferative activity in breast carcinomas have proved to be of prognostic value. Because only half of the ER-positive patients respond to endocrine therapy it is hypothesized that it might be cases with positive ER status and high proliferative activity that fail endocrine treatment. Breast cancer patients with advanced/disseminated disease (n = 109) were included in this study. No adjuvant systemic therapy was given, but when the patients developed recurrent disease they were all treated with endocrine therapy. The ER status and the proliferative activity (expressed as the ER index and MIB-1 index, respectively) were investigated retrospectively on sections from the primary tumour by immunostaining with monoclonal antibodies (anti ER-antibody and MIB-1) which are applicable on formalin-fixed, paraffin-embedded tissue after microwave pretreatment. In ER-positive tumours there was no significant difference in response to endocrine therapy between tumours with high proliferative activity and tumours with low proliferative activity. This study shows that proliferative activity does not seem to predict response to endocrine therapy but indicates that proliferative activity is capable of revealing differences in the disease free interval, irrespective of ER status.