EDITOR—Lindblom and Liljegren comment about oestrogen receptor in their clinical review of tumour markers in malignancies.1 They failed, however, to acknowledge that two isoforms of the receptor (ERa and ERb) are now known to exist and to distinguish between the two. This is important as it is now incorrect both scientifically and clinically to talk solely about ER as if it were one entity.

The oestrogen receptor that they referred to is the classical oestrogen receptor or ERa2; as noted in their table, it predicts response to endocrine treatment in the adjuvant setting and correlates with a better prognosis. Not noted in their table is that ERa immunohistochemistry is used as a diagnostic investigation in patients with metastases when there is a primary of unknown origin. Also not noted is that ERa expression does not guarantee response to endocrine treatment, with 30-40% of such tumours failing to respond.3

Oestrogen receptor β, or ERb, is the more recently discovered isoform; ERa and ERb represent two gene products with distinct biological roles and ligand binding specificity.4 With reference to the breast the expression of ERb, its role in the normal and malignant breast, the interactions between it and ERa, and its use as a tumour …