DISEASE CHARACTERISTICS:

• Histologically confirmed breast cancer

  • Locally advanced disease

    • Not amenable to curative surgery and/or radiotherapy OR

  • Metastatic disease

    • Stage IIIB, IIIC, or IV
• Measurable disease

• Presenting with de novo advanced or metastatic cancer OR tumor progression in 1 of the following ways:

  • During or after completing adjuvant tamoxifen therapy
  • During first-line metastatic therapy with tamoxifen
• Disease limited to the bone allowed provided at least 2 bone metastases exist (including at least 1 osteolytic lesion), each having a unilateral dimension of at least 1 cm
• No CNS metastases
• No hepatic metastases that constitute extensive visceral disease or are acutely life threatening
• No symptomatic pulmonary lymphangitic metastases
• No prior inflammatory breast cancer
• Must be appropriate to receive endocrine therapy as treatment for advanced disease

• Hormone receptor status:

  • Estrogen and/or progesterone receptor positive

PATIENT CHARACTERISTICS:

Age

• 18 and over

Sex

• Female

Menopausal status

• Postmenopausal defined by 1 of the following:

  • Radiation-induced menopause or surgical bilateral oophorectomy

  • Intact uterus and any of the following:

    • Older than 55 years of age
    • No menses for the past 5 years
    • 55 years of age or younger and no menses for at least the past 12 months (but has had menses in the past 5 years) and postmenopausal levels of follicle-stimulating hormone (FSH) (i.e., concentration greater than the lower limit of normal)

  • No intact uterus and either of the following:

    • Older than 55 years of age
    • 55 years of age or younger and has FSH levels in the postmenopausal range

Performance status

• ECOG 0-2

Life expectancy

• At least 6 months

Hematopoietic

• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3
• Hemoglobin at least 8.5 g/dL

Hepatic

• Bilirubin no greater than 1.5 times upper limit of normal (ULN)
• AST and ALT no greater than 3 times ULN (5 times ULN if liver metastases are present)
• Hepatitis B surface antigen negative
• Hepatitis C virus negative

Renal

• Creatinine no greater than 1.5 times ULN
• Calcium no greater than 11 mg/dL (2.75 mmol/L)

Cardiovascular

• No myocardial infarction within the past 6 months
• No unstable angina
• No known pulmonary hypertension

Other

• Not pregnant
• Negative pregnancy test
• Fertile patients must use effective contraception during and for 12 weeks after study participation
• Cholesterol no greater than 350 mg/dL (9.0 mmol/L)
• Triglycerides no greater than 400 mg/dL (4.56 mmol/L)
• Able to swallow whole tablets
• HIV negative
• Not immunocompromised
• No other malignancy within the past 5 years except appropriately treated carcinoma in situ of the cervix, basal cell or squamous cell skin cancer, or contralateral breast cancer
• No other serious concurrent illness
• No known hypersensitivity to any of the components in letrozole or CCI-779
• No other major illness that would increase the risk associated with study participation

PRIOR CONCURRENT THERAPY:

Biologic therapy

• At least 6 months since prior trastuzumab (Herceptin)
• At least 3 weeks since prior biologic therapy
• At least 3 weeks since prior immunologic therapy
• No concurrent immunotherapy
• No concurrent prophylactic use of growth factors except erythropoietic agents

Chemotherapy

• At least 6 months since prior adjuvant chemotherapy
• No prior chemotherapy for locally advanced disease or in the metastatic setting
• No concurrent cytotoxic chemotherapy
• No prior CCI-779

Endocrine therapy

• See Disease Characteristics
• At least 3 weeks since prior hormonal therapy (adjuvant or metastatic setting)
• Prior adjuvant antiestrogens allowed
• No prior aromatase inhibitors
• No other concurrent aromatase inhibitors
• No concurrent hormonal agents
• Concurrent corticosteroids for physiologic replacement allowed

Radiotherapy

• See Disease Characteristics
• At least 3 weeks since prior local radiotherapy
• No prior radiotherapy to more than 25% of the marrow

• Concurrent radiotherapy allowed with the following criteria:

  • Palliative radiotherapy allowed for pain control or other reasons with no curative intent
  • Tumor progression should be ruled out before therapy
  • No radiotherapy to more than 25% of the bone marrow
  • No radiotherapy including all of the target lesions

Surgery

• At least 3 weeks since prior surgery

Other

• At least 3 weeks since prior immunosuppressive agents
• No ongoing maintenance therapy for life-threatening ventricular arrhythmia
• No other concurrent anticancer therapy
• No other concurrent investigational therapy
• No concurrent immunosuppressive therapy
• No concurrent ketoconazole
• No concurrent phenobarbitol, carbamazepine, or phenytoin
• No concurrent Hypericum perforatum (St. John's wort)