PADA -1 (“Palbociclib and Circulating Tumor DNA for ESR1 Mutation Detection”) (NCT03079011) is an ongoing trial designed to evaluate the efficacy of a switch in ET (AI changed to fulvestrant) combined with palbociclib at the time that ESR1 mutations are detected in ctDNA on treatment [72]. This evidence concerns the gene ESR1 and neoplasm.