Inclusion Criteria:

• Women age 18 years or older
• Pathological or histological confirmation of breast cancer at initial diagnosis or at the time of metastases
• ECOG performance status of 0, 1 or 2 or Karnofsky performance status of 60 or higher
• Predicted life expectancy of 12 weeks or more
• Postmenopausal endocrine status. LH/FSH levels in the postmenopausal range in women whose menopause occurred less than 5 years ago
• Locally recurrent, locally advanced, locally metastatic disease not amenable to radiation therapy or surgery and/or distant metastatic disease
• At least one tumor localization measurable in 2 dimensions (one diameter at least 2 cm for soft tissue/visceral disease assessed by CT/MRI scan or conventional X-ray technique, one diameter at least 1 cm for bone lesions assessed by conventional X-ray techniques)
• Estrogen receptor and/or progesterone receptor positive (by laboratory/institutional standard) at the time of initial diagnosis or determined during subsequent biopsy/surgery of metastases
• Written informed consent obtained

Exclusion Criteria:

• Prior hormonal therapy to treat locally recurrent, locally advanced or metastatic disease
• Prior adjuvant therapy with aromatase inhibitors or antiestrogens/SERMs within 12 months prior to enrollment
• Progression of disease during therapy with antiestrogens (including SERMs administered for prevention of osteoporosis)
• Life-threatening locally recurrent, locally advanced or metastatic disease or disease requiring chemotherapeutic intervention (such as inflammatory breast cancer)
• History of known CNS metastases, significant neurological dysfunction including active seizures, or clinical signs of other significant neurological diseases
• Other active malignancy (except basal cell carcinoma of the skin or in situ cervical cancer). Patients with previous malignancies must be without evidence of disease for at least five years
• Renal insufficiency (serum creatinine > 2.0 mg/dL)
• Aspartate aminotransferase, alanine aminotransferase or serum bilirubin levels more than 2.5 times upper limit of normal
• Hemoglobin <9 g/dL
• Platelet count of less than 100,000 platelets per mm3
• Total white blood cell count of less than 2,000 cells per mm3
• Premenopausal endocrine status; pregnant or lactating females
• Usage of an investigational drug within the thirty (30) days prior to enrollment; or the planned usage of an investigational drug other than the study medication during the course of the current study
• Contraindication to use of toremifene, atamestane, letrozole or any of the inactive components of their formulations
• Prior enrollment in this study