Bevacizumab and Letrozole in Treating Postmenopausal Women With Locally Advanced or Metastatic Breast Cancer That Cannot Be Removed By Surgery

DISEASE CHARACTERISTICS:

* Histologically or cytologically confirmed carcinoma of the breast

  * Locally advanced or metastatic (stage IV) disease
  * Unresectable disease
* Measurable or nonmeasurable disease
* May have had stable or progressive disease after ≤ 2 prior conventional chemotherapy regimens for treatment of locally advanced or metastatic breast cancer

  * Prior chemotherapy in the adjuvant or metastatic setting is not required
  * Any number of prior neoadjuvant or adjuvant chemotherapy regimens allowed
  * Prior treatment with high-dose chemotherapy and autologous stem cell or bone marrow transplantation is considered 1 regimen when administered for metastatic disease (including induction chemotherapy and preparative regimen)
* May have had stable or responding disease on prior nonsteroidal aromatase inhibitors (e.g., letrozole, anastrozole, or aminogluthemide)

  * Any prior aromatase inhibitor-related toxicity ≥ grade 3 must have resolved ≥ 4 weeks before the start of study treatment
* May have had disease progression on other prior hormonal therapy (e.g., selective estrogen receptor modulators \[SERMs\], receptor downregulators \[SERDs\], or ovarian suppression) in the adjuvant or metastatic setting
* No history or evidence of primary brain tumor or brain metastases by CT scan or MRI
* Must have estrogen receptor- and/or progesterone receptor-positive tumor

PATIENT CHARACTERISTICS:

* Rendered postmenopausal with ovarian suppression (ovarian suppression with a depot LH-RH agonist allowed) prior to the start of study treatment OR is already postmenopausal, as defined by 1 of the criteria:

  * No spontaneous menses for ≥ 12 months if the patient is ≥ 50 years old
  * Amenorrheic for ≥ 12 months if the patient is \< 50 years old, with serum estradiol and follicle-stimulating hormone (FSH) levels within the institutional postmenopausal range
  * Bilateral oophorectomy

    * At least 28 days since surgical oophorectomy
  * Patients who have had prior hysterectomy but intact ovaries must be ≥ 55 years old, or have serum estradiol and FSH levels within the postmenopausal range
  * Ongoing ovarian suppression with a depot LH-RH agonist
* ECOG performance status (PS) 0-2 OR Karnofsky PS 60-100%
* Life expectancy \> 3 months
* Female only
* Absolute neutrophil count ≥ 1,000/mm\^3
* Platelet count ≥ 75,000/mm\^3
* WBC ≥ 2,500/mm\^3
* AST and ALT ≤ 2.5 times upper limit of normal
* Bilirubin normal
* Creatinine normal OR creatinine clearance ≥ 60 mL/min
* No proteinuria at baseline

  * Patients who unexpectedly have ≥ +1 proteinuria must undergo a 24-hour urine collection that demonstrates ≤ 500 mg of protein over 24 hours
* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception
* No presence of bleeding diathesis or coagulopathy
* No history of allergic reaction to compounds of similar chemical or biologic composition to letrozole or bevacizumab
* No serious, nonhealing wound, ulcer, or bone fracture
* No unstable angina pectoris
* No serious cardiac arrhythmia requiring medication
* No uncontrolled hypertension
* No myocardial infarction
* No New York Heart Association class II-IV congestive heart failure
* No peripheral vascular disease ≥ grade II within the past year
* No other clinically significant cardiovascular disease
* No history or evidence of other CNS disease by CT scan or MRI, including seizures not controlled with standard medical therapy or stroke
* No gastrointestinal tract disease resulting in an inability to take oral medication
* No requirement for IV alimentation
* No significant traumatic injury within the past 28 days
* No psychiatric illness or social situation that would preclude study compliance
* No other uncontrolled intercurrent illness

PRIOR CONCURRENT THERAPY:

* See Disease Characteristics
* No prior steroidal aromatase inhibitors (e.g., exemestane) unless administered in the adjuvant setting (not for metastatic disease) and ≥ 12 months have elapsed since last treatment
* Any number of prior immunotherapies (e.g., trastuzumab \[Herceptin\^®\] or vaccines) in the adjuvant or metastatic setting allowed
* More than 3 weeks since prior chemotherapy (6 weeks for nitrosoureas or mitomycin C)
* More than 3 weeks since prior radiotherapy
* More than 3 weeks since prior immunotherapy
* More than 3 weeks since prior investigational therapy
* More than 2 weeks since prior hormonal therapy except letrozole therapy or a luteinizing hormone-releasing hormone (LH-RH) agonist for ovarian suppression
* No prior surgical procedures affecting absorption
* More than 28 days since prior major surgery or open biopsy
* At least 24 hours since prior placement of indwelling catheters
* At least 10 days since prior and no concurrent full-dose oral or parenteral anticoagulants or thrombolytic agents except as required to maintain patency of preexisting, permanent indwelling IV catheters

  * Patients receiving warfarin should have INR \< 1.5
* No prior bevacizumab
* No other prior KDR inhibitors (e.g., vascular endothelial growth factor \[VEGF\] Trap, SU5416, SU6668, ZD6474, vatalanib, AEE788, or IMC-1CII)
* No other concurrent investigational agent
* No concurrent chronic daily treatment with aspirin (\> 325 mg/day) or nonsteroidal anti-inflammatory medications known to inhibit platelet function (e.g., cyclooxygenase-1 inhibitors)
* Concurrent bisphosphonates (e.g., zoledronate or pamidronate) or growth factors allowed
* No other concurrent anticancer agents or therapies