Elacestrant (RAD1901) is one such SERD that inhibits cell proliferation in ER+ BC cell lines and is being studied as part of clinical trials in ER+/HER-2 negative advanced BC where partial response as an effective SERD was demonstrated in heavily pre-treated ER+/ER mutant MBC and patients (ClinicalTrials.gov Identifier: NCT03778931 and NCT02338349) (114, 115). The gene discussed is ESR1; the disease is breast cancer.