Introduction:
Estrogen receptor (ER)-α and ER-β are believed to 				mediate the action of estradiol in target tissues. Several ER-α and 				ER-β variant messenger RNAs have been identified in both normal and 				neoplastic human tissues. Most of these variants contain a deletion of one or 				more exons of the wild-type (WT) ER messenger RNAs. The putative proteins that 				are encoded by these variant messenger RNAs would therefore be missing some 				functional domains of the WT receptors, and might interfere with WT-ER 				signaling pathways. The detection of ER-α variants in both normal and 				neoplastic human breast tissues raised the question of their possible role in 				breast tumorigenesis.
We have previously reported an increased relative expression of 				exon 5 deleted ER-α variant (ERD5) messenger RNA and of another ER-α 				variant truncated of all sequences following the exon 2 of the WT ER-α 				(ERC4) messenger RNA in breast tumor samples versus independent normal breast 				tissues. In contrast, a decreased relative expression of exon 3 deleted 				ER-α variant (ERD3) messenger RNA in tumor tissues and cancer cell lines 				versus independent normal reduction mammoplasty samples has recently been 				reported. These data were obtained in tissues from different individuals and 				possible interindividual differences cannot be excluded.