The purpose of this study is to examine the effect of the combination of everolimus and letrozole compared to placebo and letrozole as pre-surgical therapy in patients with newly diagnosed estrogen receptor positive breast cancer.

Inclusion Criteria:

• Histologically-confirmed diagnosis of invasive breast cancer, previously untreated
• Patients must be postmenopausal
• Candidates for mastectomy or breast-conserving surgery
• Primary tumor of above 2 cm diameter, measured by imaging
• Clinical Stage M0
• WHO performance status ≤1
• Adequate bone marrow, liver, and renal function

Exclusion Criteria:

• Multicentric invasive tumors
• Bilateral or inflammatory breast cancer
• Receiving concomitant anti-cancer treatments such as chemotherapy
• Patients with an uncontrolled infection
• Patients with other concurrent severe and/or uncontrolled medical disease

Additional protocol-defined inclusion/exclusion criteria may apply.