ESR1 and breast cancer: Thus, Risom and coworkers have shown that the introduction of a deregulated MYC into the murine NeuNT model of amplified-HER2 breast cancer allowed for generating tumors displaying a consistent intertumoral heterogeneity, with generation also of aggressive tumors with metaplastic histology which mimic a subtype of HER2-amplified, ER- human tumors by molecular expression [443].