Inclusion Criteria:

          -  Postmenopausal, Estrogen-receptor positive and/or Progesterone-receptor positive
             breast cancer

          -  Phase Ib dose escalation only: Any number of prior lines of endocrine therapy is
             allowed with the exception of cytotoxic therapy which is limited to one prior line
             administered in the advanced (metastatic or locally advanced) setting.

          -  Phase Ib dose expansions Arms 1, 2 and 3

          -  No prior systemic treatment in the advanced (metastatic or locally advanced) setting
             with the exception of treatment with letrozole for a maximum of one month prior to
             starting study treatment.

          -  Patients who received (neo)adjuvant therapy for breast cancer are eligible. Prior
             therapy with letrozole or anastrozole in the (neo)adjuvant setting is permitted if the
             disease-free interval is greater than 12 months from the completion of treatment.

        Exclusion Criteria:

          -  HER2-overexpression in the patient's tumor tissue

          -  Patients with active CNS or other brain metastases

          -  Major surgery within 2 weeks

          -  Acute or chronic pancreatitis

          -  Bilateral diffuse lymphangitic carcinomatosis

          -  Another malignancy within 3 years

          -  Receiving hormone replacement therapy that cannot be discontinued

          -  Impaired cardiac function

          -  Patients with clinically manifest diabetes mellitus (treated and/or clinical signs or
             with fasting glucose ≥ 126 mg/dL / 7.0 mmol/L or hemoglobin A1c >6.5%), history of
             gestational diabetes mellitus or documented steroid-induced diabetes mellitus.

          -  Other protocol-defined inclusion/exclusion criteria may apply