OP-1250 (Palazestrant) is an oral CERAN that induces the function of SERD, that is, degradation of ER and inhibition of estrogen-stimulated breast cell proliferation and receptor degradation (ER Antagonist OP-1250 Demonstrates Continued Anti-Tumor Activity in Advanced ER+ HER2– Breast Cancer, 2023; Hodges-Gallagher et al., 2020). This evidence concerns the gene ESR1 and breast cancer.