Indeed, the concerted efforts of different academic consortia such as the National Cancer Institute (NCI) PDXNet, EurOPDX and the International Breast Cancer PDX consortium have resulted in a (still growing) collection of over 500 stably transplantable PDX models representing all three clinical subtypes of breast cancer (ER + , HER2 + , and "triple-negative" (TNBC) breast cancer) [67, 68]. This evidence concerns the gene ESR1 and breast cancer.