ESR1 and gastric cancer: Interestingly, the addition of 5-FU facilitated the suppressive effect of exemestane.[7] Another agent, fulvestrant, an analog of E2 that downregulates and degrades ERα, also demonstrated anti-neoplastic efficacy on GC cells.[8] E2 enhanced the proliferation of ER-positive GC cell lines, while the administration of fulvestrant repressed the proliferative effect of E2.