The estrogen receptor gene (ESR1) is highly amplified in some breast cancer patients; ESR1 amplification is accompanied by high protein expression, but only two-thirds of ER-overexpressing patients show ESR1 amplification;

The efficacy of monotherapy with estrogen therapy (tamoxifen) in patients with ESR1 amplification was significant, with overall survival significantly longer than in patients without ERS1 amplification, and the higher the degree of amplification, the better the prognosis;

Testing and treatment targeting the estrogen receptor gene is more accurate and effective than for its protein;

Some patients with benign and precancerous breast cancer also showed expression of the ESR1 gene, suggesting that amplification of the ESR1 gene may be an early event in the development of breast cancer.