Regional cyclin D1 overexpression or hypoxia correlate inversely with heterogeneous oestrogen receptor-alpha expression in human breast cancer.

The oestrogen receptor-alpha (ER alpha) differs in expression and regulation in breast cancer and, by studying the co-factor cyclin D1 as well as changes in the microenvironment, we here delineate two conditions that potentially cause regional down-regulation of the receptor. Heterogeneously expressed ER alpha was observed in 24 out of 134 of the studied breast cancer samples. In 6 out of 24 of the heterogeneous tumours, there was a clear inverse association between cyclin D1 protein/gene amplification and presence of ER alpha.