Besides the detection in metastatic tissue, several studies have also interrogated the presence of these mutations in circulating tumor DNA (ctDNA) in institutional cohorts15,21,22 or in the context of clinical trials.23–25 The prevalence of ESR1 mutations was much higher here, ranging between 14.8 and 31.5% in the institutional series and between 25.3 and 39.1% in the trials. The gene discussed is ESR1; the disease is neoplasm.