1. ¹Department of Biochemistry & Medical Genetics, Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba, Canada R3E OV9
2. ²Department of Pathology, University of Manitoba, Winnipeg, Manitoba, Canada R3E OV9

Correspondence: LC Murphy, E-mail: lcmurph@cc.umanitoba.ca

Received 17 January 2006; Revised 30 May 2006; Accepted 29 June 2006; Published online 1 August 2006.

Abstract

To analyse the phenotype of breast tumours that express oestrogen receptor- (ER) alone tissue microarrays were used to investigate if ER isoforms are associated with specific prognostic markers and gene expression phenotypes in ER-negative tumours. ER-negative tumours were positive for ER1 in 58% of cases (n=122/210), total ER in 60% (n=115/192) and ER2/cx in 57% of cases (n=114/199). Oestrogen receptor-1 and total ER were significantly correlated with Ki67 (r=0.28, P<0.0001, n=209; r=0.29, P<0.0001, n=191) and with CK5/6, a marker of the basal phenotype (r=0.20, P=0.0106, n=170; r=0.18, P=0.0223, n=158). ER2/cx was strongly associated with p-c-Jun and NF-Bp65 (r=0.53, P<0.0001, n=93; r=0.35, P<0.0001, n=176). This study shows that a range of ER isoform expression occurs in ER-negative breast tumours. While expression of ER1, total and ER2/cx are correlated, individual forms show associations with certain phenotypes that suggest different roles in subsets of ER-negative cancers. Based on our in vivo observations, ER may have the potential to become a therapeutic target in the specific subcohort of ER-negative breast cancers.