Circulating biomarkers and resistance to endocrine therapy in metastatic breast cancers: correlative results from AZD9496 oral SERD phase I trial.

Abstract

Common resistance mechanisms to endocrine therapy (ET) in estrogen receptor (ER) positive metastatic breast cancers include, among others, ER loss and acquired activating mutations in the ligand-binding domain of the ER gene (ESR1LBDm). ESR1 mutational mediated resistance may be overcome by selective ER degraders (SERDs). During the first-in-human study of oral SERD AZD9496, early changes in circulating tumor cells (CTC) and circulating tumor DNA (ctDNA) were explored as potential non-invasive tools, alongside paired tumor biopsies, to assess pharmacodynamics and early efficacy.