ESR1 and breast neoplasm: The current study investigated the activity of LAS in a letrozole-resistant breast tumor model that does not have ESR1 mutations.<h4>Methods</h4>Letrozole-resistant, MCF7 LTLT cells tagged with luciferase-GFP were injected into the mammary duct inguinal glands of NSG mice (MIND model; 6 mice/group).