ESR1 and breast neoplasm: Given that ENDX at 5 μM displayed promising antitumor activity in cell line models harboring activating PIK3CA mutations, which occur in nearly 40% of patients with advanced ERα+/HER2- breast cancer43 and are associated with poor survival outcomes44, further studies are ongoing to evaluate the clinical activity of ENDX therapy in breast tumors harboring PIK3CA mutations.