Coexpression of estrogen receptor alpha and beta: Poor prognostic factors in human breast cancer?

The cloning of a second estrogen receptor (ER), ER beta, has prompted a ree valuation of the role of ERs in breast cancer. The aim of this study was to determine the expression of both ER isoforms in normal (n = 23) and malign ant (n = 60) human breast tissue by reverse transcription-PCR and correlate this information with known prognostic factors including tumor grade and n ode status, In normal breast tissue, expression of ER beta predominated, wi th 22% of samples exclusively expressing ER beta; this was not observed in any of the breast tumor samples investigated, Most breast tumors expressed ER alpha, either alone or in combination with ER beta. Interestingly, those tumors that coexpressed ER alpha and ER beta were node positive (P = 0.02; Fisher's exact test) and tended to be of higher grade. Because antiestroge ns are agonists when signaling through the AP1 element, overexpression of E R beta in tumors expressing both ER subtypes mag explain the failure of ant iestrogen therapy in some breast cancer patients. Thus, ER beta may be a us eful prognostic factor in patients with breast cancer.