Alterations and Polymorphisms of the Estrogen Receptor Gene in Breast Cancer.
The existence of hormone-independent tumors is a substantial problem for the present endocrine treatment of breast cancers. Recently, numerous variant estrogen receptors (ERs) at the mRNA level have been detected with base pair insertions, transitions, and deletions, as well as alternative splicing, yielding deletion of exon 3, 5, or 7. It has been shown that the loss of hormone dependence in breast tumors is partly due to the presence of mutated or truncated ERs that can activate the transcription of an estrogen-regulatable gene in the absence of estrogen. The mechanism of the loss of hormone dependency is, however, still very complex. Thus, further work assessing the correlation between clinical behavior and ER variants is required to determine whether these variants play a role in hormone-resistant disease. Additionally, a possible linkage to the ER gene has been found in some breast cancer families, suggesting that either the ER gene itself or an adjacent gene may be breast cancer susceptibility genes.
Iwase
H
Department of Surgery II, Nagoya City University Medical School, 1 Kawasumi, Mizuho-ku, Nagoya 467, Japan.
Kobayashi
S