Study of Letrozole With or Without BYL719 or Buparlisib, for the Neoadjuvant Treatment of Postmenopausal Women

Inclusion Criteria:

1. Patient is an adult, female ≥ 18 years old at the time of informed consent
2. Patient has a histologically and/or cytologically confirmed diagnosis of breast cancer
3. Patient is postmenopausal.
4. Patient has T1c-T3, any N, M0, operable breast cancer
5. Patients must have measurable disease
6. Patient has diagnostic biopsy available for the analysis of PIK3CA mutation and Ki67 level.
7. Patient has estrogen-receptor and/or progesterone positive breast cancer as per local laboratory testing
8. Patient has HER2 negative breast cancer defined as a negative in situ hybridization test or an IHC status of 0 or 1+ as per local laboratory testing

Exclusion Criteria:

1. Patient has locally recurrent or metastatic disease
2. Patient has received any systemic therapy (e.g. chemotherapy, targeted therapy, immunotherapy) or radiotherapy for current breast cancer disease before randomization.
3. Patient with type 1 diabetes mellitus or not adequately controlled type 2 diabetes mellitus
4. History of acute pancreatitis within 1 year of study entry
5. Uncontrolled hypertension