Phase III Study of Atamestane Plus Toremifene Versus Letrozole in Advanced Breast Cancer

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