Study of Safety and Efficacy of Letrozole Monotherapy as Second-line Endocrine Therapy in Postmenopausal Patients With Advanced Breast Cancer Who Received Previous Anti-estrogen Treatment

Inclusion Criteria: * Patients with histologically or cytologically documented breast cancer * Patients with progressive breast cancer (advanced breast cancer, locoregional recurrence not operative, or metastatic breast cancer) * Patients with hormone receptor (ER and/or PgR) positive or both unknown. * Postmenopausal patients between ages 20 and 79 years, inclusive * Patients with a history of adjuvant therapy or advanced breast cancer treated with anti-estrogens * Patients with documented measurable or evaluable lesions. * Patients with sufficient organ function to evaluate the safety * Patients whose performance status (PS) is 0～2 Exclusion Criteria: * Patients with diffuse lymphangitis carcinomatosa of the lung or CNS involvement, liver metastasis occupying more than one third of the liver, or inflammatory breast cancer * Patients with other concurrent or previous malignant disease (excluding contralateral breast cancer, in situ carcinoma of cervix uteri, and adequately treated basal or squamous cell carcinoma of the skin) * Patients in whom one of the following is the sole manifestation of disease: hilar enlargement, pleural effusion and ascites * Patients with only blastic bone metastases or a mixed blastic and lytic bone metastases at the same site and no other measurable or evaluable lesions * Patients with serious current disease such as uncontrolled cardiac diseases and/or uncontrolled diabetes mellitus by any medications (including a historical serious cardiac disease) * Patients with adrenal insufficiency (treated or untreated) or Cushing's syndrome * Patients with any of the following previous treatments 1. Chemotherapy for metastatic and/or locoregional recurrent disease 2. Previous adjuvant endocrine therapy other than ovariectomy, anti-estrogen treatment, LH-RH analogues or radiation castration 3. Previous first-line endocrine therapy (e.g., aromatase inhibitors and gastagens) for the treatment of metastatic and/or locoregional recurrent breast cancer other than anti-estrogen or LH-RH analogues treatment 4. Patients who have not recovered from toxicity caused by previous therapy 5. For patients on investigational drugs, adequate wash-out periods of at least 7 days in the case of topical investigational drugs and at least 30 days in the case of systemic 6. Previous bisphosphonate therapy started within 6 months without any other measurable or evaluable lesions 7. Patients who have not stopped treatment with other anti-estrogen or anti-cancer drugs (other than bisphosphonates) before starting the trial medication Other protocol-defined inclusion/exclusion criteria may apply.