ESR1 and breast cancer: Rapalogs are currently approved for treatment of ER+ advanced breast cancer, metastatic renal cell carcinoma, subependymal giant cell astrocytoma, and progressive neuroendocrine tumors of pancreatic origin.55,56 Although everolimus and other mTORC1 inhibitors have demonstrated statistically significant responses with improved progression-free survival, these responses are usually short-lived and rarely induce sustained disease remission, due to the emergence of resistance.