A slightly different switching approach was explored in the PAlbociclib and circulating tumor DNA for ESR1 mutation detection (PADA)-1 trial in which patients with rising ESR1 mutations (a molecular mechanism of resistance to AI therapy) detected in circulating tumor DNA during first-line AI and palbociclib therapy were randomly assigned either to continue the same treatment or to switch to fulvestrant with palbociclib. The gene discussed is ESR1; the disease is neoplasm.