Discussion:
A statistically significant higher ERC4 messenger RNA expression 				was found in ER-positive/PR-positive tumors as compared with matched normal 				breast tissues. ERC4 variant messenger RNA has previously been demonstrated to 				be more highly expressed in ER-positive tumors that showed poor as opposed to 				tumors that showed good prognostic characteristics. Interestingly, we also have 				reported similar levels of expression of ERC4 messenger RNA in primary breast 				tumors and their concurrent axillary lymph node metastases. Taken together, 				these data suggest that the putative role of the ERC4 variant might be 				important at different phases of breast tumorigenesis and tumor progression; 				alteration of ERC4 messenger RNA expression and resulting modifications in ER 				signaling pathway probably occur before breast cancer cells acquire the ability 				to metastasize. Transient expression assays revealed that the protein encoded 				by ERC4 messenger RNA was unable to activate the transcription of an 				estrogen-responsive element-reporter gene or to modulate the wild-type ER 				protein activity. The biologic significance of the changes observed in ERC4 				messenger RNA expression during breast tumorigenesis remains to be 				determined.
A higher relative expression of ERD3 messenger RNA in the normal 				breast tissue components compared with adjacent neoplastic tissue was found in 				the ER-positive subgroup. These data are in agreement with the recently published report of 				Erenburg et al, who showed a decreased relative expression of ERD3 				messenger RNA in neoplastic breast tissues compared with independent reduction 				mammoplasty and breast tumor. Transfection experiments showed that the 				activation of the transcription of the pS2 gene by estrogen was drastically 				reduced in the presence of increased ERD3 expression. The authors hypothesized 				that the reduction in ERD3 expression could be a prerequisite for breast 				carcinogenesis to proceed.
We observed a significantly higher relative expression of ERD5 				messenger RNA in breast tumor components compared with matched adjacent normal 				breast tissue. These data confirm our previous observations performed on 				unmatched normal and neoplastic human breast tissues. Upregulated expression of 				this variant has already been reported in ER-negative/PR-positive tumors, as 				compared with ER-positive/PR-positive tumors, suggesting a possible correlation 				between ERD5 messenger RNA expression and breast tumor progression. Even though 				it has been suggested that ERD5 could be related to the acquisition of 				insensitivity to antiestrogen treatment (ie tamoxifen), accumulating data 				refute a general role for ERD5 in hormone-resistant tumors. Only ER-positive 				pS2-positive tamoxifen-resistant tumors have been shown to express 				significantly higher levels of ERD5 messenger RNA, as compared with control 				tumors. Taken together, these data suggest that the exact biologic significance 				of ERD5 variant expression during breast tumorigenesis and breast cancer 				progression, if any, remains unclear.
In conclusion, we have shown that the relative expressions of ERC4 				and ERD5 variant messenger RNAs were increased in human breast tumor tissue, as 				compared with normal adjacent tissue, whereas the expression of ERD3 variant 				messenger RNA was decreased in breast tumor tissues. These results suggest that 				the expressions of several ER-α variant messenger RNAs are deregulated 				during human breast tumorigenesis. Further studies are needed to determine 				whether these changes are transposed at the protein level. Furthermore, the 				putative role of ER-α variants in the mechanisms that underlie breast 				tumorigenesis remains to be determined.