ESR1 and breast cancer: Elacestrant (RAD1901) is the first oral selective ER degrader demonstrating a significant progression-free survival (PFS) improvement compared to the standard-of-care (SOC) endocrine monotherapy both in the overall population and in patients with ESR1 mutations, with manageable safety in a phase III trial (EMERALD) for patients with ER+/HER2− advanced BC or MBC [88].