The primary objective of this study is to assess the feasibility and accuracy of a new multi-gene next-generation sequencing (NGS) panel designed to identify genomic alterations in AKT1, ERBB2, ESR1, KRAS, PIK3CA, and TP53 genes in circulating tumor DNA (ctDNA) extracted from the plasma of women receiving hormonal therapy (HT) and CDK4/6i. This evidence concerns the gene ESR1 and neoplasm.