Oestrogen receptor β and neoadjuvant therapy with tamoxifen: prediction of response and effects of treatment

In order to elucidate the relative importance of oestrogen receptor (ER)α, ERβ and an ERβ variant (ERβ2/βcx) in the response of breast cancers to tamoxifen, tumour levels of each receptor were assessed in 36 patients before and after 3 months of neoadjuvant treatment with tamoxifen (20 mg daily). All patients were postmenopausal women presenting with large ERα-positive breast cancers. Clinical response to treatment was assessed by tumour volume changes as determined from sequential ultrasounds and pathological response by comparison of the tumour morphology before and after treatment. Of 33 cases, 23 (70%) were classified as having a clinical response and 16 (48%) as having a response pathologically. All tumours stained positively for ERα and ERβ and 15 out of 33 (45%) for ERβ2/βcx. There were no significant differences in quantitative expression of any receptor between tumours that subsequently responded and that did not, whether response was assessed clinically or pathologically. Tamoxifen treatment was associated with a decrease in ERα, but an increase was the most frequent change (17 out of 33) in ERβ, and no consistent change was evident in staining of the ERβ2/βcx variant. In summary, ERβ1 and ERβ2/βcx variant protein are detected in ERα-positive breast tumours but their expression is not associated with a response to tamoxifen. Differential changes in ERα and ERβ were seen with treatment.