Estrogen receptor alpha (ESR1) mutant A908G is not a common feature in benign and malignant proliferations of the breast.

Alterations in estrogen responsive pathways are thought to contribute to benign and malignant breast disease. It has been reported previously that more than a third of typical epithelial hyperplasia lesions harbor the missense mutation A908G in the estrogen receptor alpha (ESR1) gene. This substitution of an arginine for a lysine at codon 303 was reported to confer mitogenic hypersensitivity to estrogen. To explore this finding further, we analyzed ESR1 for this mutation in a series of breast tissues ranging from typical hyperplasia to invasive cancer. In contrast to previous studies, no evidence for this mutation was found in 36 invasive cancers, 11 in situ carcinomas, 14 epithelial hyperplasias with atypia, 11 epithelial hyperplasias without atypia, and 11 breast cancer cell lines. These results indicate that ESR1 mutant A908G does not occur with significant frequency in either benign or malignant proliferations of breast epithelia.