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