A Study of R1507 in Combination With Letrozole in Postmenopausal Women With Advanced Breast Cancer

Inclusion Criteria: * postmenopausal female patients; * stage IV or locally advanced breast cancer; * measurable disease; * letrozole failure (Part 2); * Eastern Cooperative Oncology Group (ECOG) performance status \<=2. Exclusion Criteria: * previous chemotherapy for metastatic breast cancer; * concurrent antibody or immunotherapy for advanced disease, within 4 weeks prior to receipt of study drug; * history of primary malignancy in 5 years prior to study, excluding adequately treated basal or squamous cell cancer of skin, or cancer in situ of cervix; * concurrent radiotherapy, or radiotherapy within 28 days prior to receipt of study drug.