A 2-Week Ketogenic Diet in Combination With Letrozole to Modulate PI3K Signaling in ER+ Breast Cancer

Primary Objective: • To evaluate the feasibility and tolerability of a 2 week ketogenic diet in combination with endocrine therapy prior to surgery for early stage ER+ breast cancer. Secondary Objectives * To determine whether endocrine therapy in combination with a dietary intervention to reduce insulin pathway signaling results in enhanced inhibition of cancer cell proliferation (measured byKi67) * To determine the effectiveness of 2 weeks of a ketogenic diet to reduce measures of insulin/PI3Kpathway activation in breast tumors * To measure changes in weight and body composition after 2 weeks of a ketogenic diet * To measure changes in insulin resistance after 2 weeks of a ketogenic diet * To measure the effectiveness of a ketogenic diet in combination with endocrine therapy to induce and maintain a ketogenic state. Outline: Participants will have baseline metabolic parameters measured and will begin a 2-week diet consisting of meal replacement shakes to induce a ketogenic state. Patients will also receive letrozole 2.5 mg daily. At the end of 2 weeks, metabolic parameters will again be measured and patients will proceed with surgical treatment of their breast cancer. A tumor biopsy from the surgical specimen will be obtained to measure cell proliferation compared with the pre-treatment diagnostic biopsy.