ESR1 and breast cancer: To further compare breast cancer cell response to carfilzomib, we utilized breast cancer patient-derived xenograft (PDX) models of various subtypes and treated them with 10 nM carfilzomib in basal-like TNBC (BCM-2277, BCM-3887) and luminal ERα+, PR+ positive PDX lines (HCI-011, HCI-013, and BCM-5097).