ESR1 and breast cancer: Three trials test the efficacy of a CDK4/6 inhibitor and endocrine therapy in ctDNA-positive patients with resected luminal BC (NCT04567420, NCT03285412, NCT04985266), while TREAT-ctDNA will use ctDNA to randomize patients to the selective estrogen receptor degrader (SERD) elacestrant or standard endocrine therapy (NCT05512364).