Figure 5. Functional validation of novel ESR1 p.A569S mutation demonstrates modest estradiol sensitivity and increased tamoxifen agonist activity.

A. Summary of ESR1 mutations detected in Patient #2 from tissue, CTC-DNA, and cfDNA in schematic representation of the encoded ERα with the LBD and F domains indicated; B. MCF-7 ESR1 A569S are more sensitive to estradiol after 5 days when assessed by crystal violet assay. Inset table indicates EC₅₀ of estradiol in pM; C. Tamoxifen has increased agonist activity in MCF-7 cells over-expressing ER-A569S. Inset table indicates maximal growth at 100nM tamoxifen. Assays were performed in triplicates with P-values error bars (standard error) indicated.