ESR1 and breast cancer: In a prospective–retrospective study on archival plasma samples from the SoFEA and PALOMA3 trials, breast cancer patients with detected baseline ESR1 mutations from plasma had improved progression-free survival (PFS) after being treated with fulvestrant (estrogen receptor antagonist) compared with exemestane (aromatase inhibitor), while patients with wildtype ESR1 had similar PFS after receiving either treatment [75].