Supplementary Figure S4 from Palazestrant (OP-1250), A Complete Estrogen Receptor Antagonist, Inhibits Wild-type and Mutant ER-positive Breast Cancer Models as Monotherapy and in Combination

OP-1250 demonstrates potent in vivo activity and outperforms competitor compounds in ESR1 mutant xenograft studies. A, Percent change in tumor volume of individual animals in listed treatment groups at day 29 of the ESR1Y537S HCI-013 PDX study, normalized to day 1 tumor volume. B, Mean and SEM tumor volume over time with listed treatments in the ESR1Y537S HCI-013EI PDX breast cancer model conducted in the absence of estrogen supplementation. The dotted line represents tumor stasis. C, Percent change in tumor volume of individual animals in listed treatment groups at day 29 of the ESR1Y537S PDX HCI-013EI xenograft study conducted in the absence of estrogen supplementation, normalized to day 1 tumor volume. D, Percent change in tumor volume of individual animals in listed treatment groups at day 29 of the ESR1Y537S ST941 PDX study, normalized to day 1 tumor volume. E, Representative ST941 PDX study immunostained tumor images of Ki67 and ER⍺ treated with vehicle, OP-1250 at 5 mg/kg, and OP-1250 at 10 mg/kg.