ESR1 and breast cancer: Disregarding the cancer type and background, including ATM, BRCA2 and p53 mutations or PTEN (phosphatase and tensin homolog) loss, the inhibition of BCA2 by either anti-ERα endocrine therapy or anti-BCA2 gene therapy holds promise for the neoadjuvant treatment of breast cancers as most of them possess functional BCA2.