Comparison of variant expression of estrogen receptor mRNA in normal breast tissue and breast cancer.

To investigate whether estrogen receptor abnormalities are associated with resistance of breast cancer to endocrine therapy, we compared estrogen receptor mRNA between normal breast tissue and carcinoma. Using the RT-PCR, paired cancer and normal breast tissue specimens from 15 patients were analyzed. Exon-deleted variants were found in both tumor and normal tissue, with differences of variant expression between normal and tumor tissue being observed. One patient showed multiple deletions in the hormone-binding domain. Alterations in the amount and/or kind of variant ER expression may be important in determining the response of breast cancer to endocrine therapy.