Is the negative prognostic value of high oestrogen receptor (ER) levels in postmenopausal breast cancer patients due to a modified ER gene product

Abstract Recently, it was found that, among post menopausal breast cancer patients receiving no adjuvant therapy, the highest oestrogen receptor (ER) levels (ER ++ ) as opposed to the intermediate ER levels (ER + ) indicated a poorer prognosis in terms of recurrence-free survival (Thorpe et al. Eur J Cancer 1993, 29A, 971–977). In the present study, we confirm, in a series of 218 node negative, postmenopausal patients in whom ER was determined using a one-dose saturating method, that ER + tumours have a more negative effect on disease-free survival (DFS) than ER + tumours ( P = 0.02). In another series of 87 ER positive, postmenopausal patients, we found a significant correlation ( P = 0.04) between the ER level and ER + R ratio (ER protein/ER-specific mRNA): the higher the ER level, the more numerous the high ER + R ratio cases (ER + R > 1.5), reflecting an imbalance between the ER protein level and ER-specific mRNA. From these results, we hypothesise that high ER levels related to a high ER + R ratio suggest the presence of a modified ER gene product.