Finally, with respect to the effects of ER antagonist treatment on the growth of ESR1 mutant expressing cells, our results are consistent with MCF7 xenograft models that show AZD9496 to be a more effective inhibitor of tumor growth in vivo compared to fulvestrant while also demonstrating increased resistance of the Y537S mutation to is ER antagonist treatment compared to the D538G mutation37,39,55. This evidence concerns the gene ESR1 and neoplasm.