ESR1 and cancer: To assess the utility of subtyping methods as predictive tools for therapeutic response, we integrated drug screening data for 555 anti‐cancer compounds (NCI NExT Oncology Interrogation Tools Library)60 targeting cancer‐relevant pathways across 18 TNBC and 5 ER+ clinically typed PDX models with projected proportions of cells categorised by SCSubtype and TNBCtype subtyping methodologies.