BYL719 and Letrozole in Post-Menopausal Patients With Hormone Receptor-Positive Metastatic Breast Cancer

This phase I trial studies the side effects and best dose of the PI3K inhibitor BYL719 when given together with letrozole in treating patients with hormone receptor-positive metastatic breast cancer. The PI3K inhibitor BYL719 may stop the growth of tumor cells by blocking some of the proteins needed for cell growth. Hormone therapy using letrozole may fight breast cancer by blocking the use of estrogen by the tumor cells. Giving the PI3K inhibitor BYL719 together with letrozole may kill more tumor cells