ESR1 and breast cancer: In this study, we examined the effects of combining ATX-101 with an EGFR/HER2/VEGFR inhibitor (AEE788) in vitro and in vivo in an orthotopic syngeneic HER2-/progesterone receptor - (PR-), estrogen receptor + (ER+)/EGFR+ mixed luminal/basal breast cancer mouse model [26-28].