Oestrogen receptors α and β show different associations to clinicopathological parameters and their co-expression might predict a better response to endocrine treatment in breast cancer

Aims: The majority of all breast cancers are hormone responsive, traditionally defined by the expression of oestrogen receptor (ER) alpha and/or progesterone receptors. In contrast to ER alpha, the clinical significance of the relatively recently identified ER beta is still unclear. This study aimed to define the relationship between ER beta and clinicopathological parameters in a mixed cohort of breast cancer and, furthermore, to investigate the impact of ER beta expression on disease outcome. Methods: The immunohistochemical expression of ER alpha and ER beta was analysed in tissue microarrays containing a total number of 512 tumours with all incident breast cancers diagnosed at the Malmo University Hospital between 1988 and 1992. Results: 78% of the tumours were ER alpha positive and 50% were ER beta positive. ER beta correlated positively with ER alpha (p = 0.001). In contrast to ER alpha, ER beta was not associated with any important clinicopathological variables. Furthermore, no overall prognostic significance could be demonstrated for ER beta. In the ER alpha-positive subgroup, however, a low expression of ER beta correlated with a decreased disease-free survival in patients receiving endocrine treatment (p = 0.003). Conclusions: Although interrelated, ER alpha and ER beta seem to be differentially associated to clinicopathological parameters, and this would support the fact that they might have different functions in vivo. Furthermore, ER beta might be a predictive marker of response to endocrine therapy, although this needs to be confirmed in additional studies, preferably randomised trials.