Elacestrant is a SERD which has been shown to induce degradation of ER, inhibit ER-mediated signaling and growth of ER+ BC cell lines in vitro and in vivo, and inhibit tumor growth in multiple patient-derived xenograft (PDX) models, including demonstrable anti-tumor activity both when applied as a single agent and in combination with palbociclib in two PDX BC models harboring ESR1 mutations [73]. The gene discussed is ESR1; the disease is breast cancer.