However, after patients experienced their first relapse, 5.3% (2/38) of them had mutated ESR1 in ctDNA, and when the metastatic tumor was treated for the first time, 33% (7/21) of the patients receiving AI had mutated ESR1 in ctDNA, compared to zero patients who received chemotherapy. This evidence concerns the gene ESR1 and metastatic neoplasm.