The phase III SERENA-6 trial evaluates a switch to camizestrant plus the same CDK4/6i versus the continuation of a nonsteroidal AI plus CDK4/6i (palbociclib or abemaciclib) in an HR+/HER2− advanced or relapsed breast cancer population who have measurable ESR1 mutations in ctDNA during first-line treatment before clinical/radiological progression (NCT04964934) [125]. Here, ERBB2 is linked to breast carcinoma.