Bevacizumab + Endocrine Treatment vs Endocrine Treatment as First Line Treatment in Postmenopausal Patients With Advanced or Metastatic Breast Cancer

Inclusion Criteria:

1. Before starting the specific protocol procedures, the written informed consent must be obtained and documented.
2. Women ≥ 18 years.
3. Capacity to comply with all the protocol requirements.
4. Functional ECOG status of 0 or 1.
5. Life expectancy ≥ 24 weeks.
6. Histologically confirmed breast adenocarcinoma, with measurable or non-measurable, locally advanced or metastatic (stage IV) disease. In the event that the patient only has locally advanced disease, she will not be able to undergo curative local treatment. Patients with metastasis confined to the bone can be chosen, but the disease must be confirmed by radiology, CT scan or NMR if there is any doubt after a single bone scan.
7. Patients with HER2-negative disease evaluated by IHC and FISH/CISH (IHC 0 or 1+, or 2+ and negative FISH). Patients with 3+ by IHC cannot be chosen regardless of the FISH/CISH status and those with positive FISH/CISH (> 2 amplifications) cannot be chosen either, regardless of the IHC findings.
8. Positive hormone receptors (estrogen receptor [ER] and/or progesterone receptor [PgR]) evaluated by a local or central laboratory, according to the criteria of the participating institution.
9. Patients who are candidates for receiving first-line treatment with letrozole.
10. Patients may have received (neo)adjuvant chemotherapy, provided that the last dose of the latter was received at least 12 months before randomization . Patients must be recovered from toxicity.

11. The patients are allowed to have received adjuvant radiotherapy, provided that it was completed at least 6 weeks before randomization and the patient has recovered from the reversible acute effects of the radiation. The previous administration of radiotherapy to palliate the pain of bone metastases is authorized, provided that:

    • Not more than 30% of bone marrow has been irradiated.
    • The patient has recovered from the reversible acute effects of the radiation.
    • The patient has at least one metastatic location which has not been irradiated and which may be evaluated for progression, or a clear progression of the bone disease has been objectified after the end of the palliative radiotherapy.

Exclusion Criteria:

1. Evolutionary disease requiring an immediate treatment with cytotoxic chemotherapy according to the investigator's judgment.
2. Patients with locally advanced breast cancer who are expected to undergo surgery or curative radiotherapy.
3. Previous chemotherapy or hormonotherapy for the metastatic disease. Patients may have received neoadjuvant chemotherapy or neoadjuvant hormonotherapy with curative intention as a part or as an alternative to an adjuvant treatment. For the previous neoadjuvant hormonotherapy the same premises than for the adjuvant hormonotherapy are valid.
4. Previous therapy with anti-VEGF or VEGFR tyrosine-kinase inhibitors.
5. History of another pathology that may affect the development of the protocol or the interpretation of results. It is considered that patients who have suffered from a skin carcinoma that is not melanoma, cervical carcinoma in situ or another neoplasia treated with a curative intention and with a disease-free interval exceeding 5 years can be chosen.
6. Evidence of CNS metastasis. A CT scan or brain NMR must be done within the 4 weeks before the randomization in case of suspecting brain metastasis.
7. History or evidence in the physical or neurological examination of CNS pathology unrelated to cancer unless it is suitable treated with standard therapy (e.g. uncontrolled convulsions).
8. History of peripheral neuropathy NCI CTCAE grade >2 at the time of randomization.
9. Patients subjected to major surgical procedures, open biopsies or those having significant trauma injuries within the 28 days prior to randomization, or patients who are expected to undergo a major surgical procedure that must necessarily be performed within the course of the study.