 This is an investigational study. Everolimus is FDA approved and commercially available to treat kidney, breast, and pancreatic cancers. Letrozole is FDA approved and commercially available to treat breast cancer and ovarian cancer. Ribociclib is not FDA approved or commercially available. It is currently being used for research purposes only. The combination of everolimus, letrozole, and ribociclib to treat endometrial cancer is investigational. 