About 30% of BC patients had detectable ESR1 mutations in blood after endocrine therapies, and several groups showed that ESR1 mutations in ctDNA samples were associated with treatment resistance and aggressive clinical behavior in these patients (Chandarlapaty et al., 2016; Gerratana et al., 2019; Schiavon et al., 2015). This evidence concerns the gene ESR1 and breast cancer.