Abstract

Aims: The majority of all breast cancers are hormone responsive, traditionally defined by the expression of oestrogen receptor (ER) α and/or progesterone receptors. In contrast to ERα, the clinical significance of the relatively recently identified ERβ is still unclear. This study aimed to define the relationship between ERβ and clinicopathological parameters in a mixed cohort of breast cancer and, furthermore, to investigate the impact of ERβ expression on disease outcome.

Methods: The immunohistochemical expression of ERα and ERβ was analysed in tissue microarrays containing a total number of 512 tumours with all incident breast cancers diagnosed at the Malmö University Hospital between 1988 and 1992.

Results: 78% of the tumours were ERα positive and 50% were ERβ positive. ERβ correlated positively with ERα (p = 0.001). In contrast to ERα, ERβ was not associated with any important clinicopathological variables. Furthermore, no overall prognostic significance could be demonstrated for ERβ. In the ERα-positive subgroup, however, a low expression of ERβ correlated with a decreased disease-free survival in patients receiving endocrine treatment (p = 0.003).

Conclusions: Although interrelated, ERα and ERβ seem to be differentially associated to clinicopathological parameters, and this would support the fact that they might have different functions in vivo. Furthermore, ERβ might be a predictive marker of response to endocrine therapy, although this needs to be confirmed in additional studies, preferably randomised trials.