Remarkably, distinct technological approaches were adopted in the aforementioned trials: the former was built on a comprehensive next generation sequencing (NGS) assay (Guardant360® CDx, GuardantHealth, CA, USA) able to simultaneously detect clinically informative molecular alterations across 55 cancer related genes from liquid biopsy specimens, including ESR1 activating mutations (310–547 codons); the latter on customized digital droplet PCR (ddPCR) assays to analyze four hotspot mutations covering 90.0 % of most frequent ESR1 actionable alterations [2,11]. Here, ESR1 is linked to cancer.