Exemestane Versus Anastrozole as First Line Hormone Therapy in Postmenopausal Metastatic Breast Cancer Patients

Inclusion Criteria:

* Pathological diagnoses of breast cancer.
* Postmenopausal women, defined as:

  * Bilateral surgical oophorectomy or amenorrhoea \>= 5 years;
  * Age \>= 56 years old and amenorrhoea \>= 1 year;
  * Chemotherapy induced amenorrhoea \>= 2 years;
  * Radiotherapy induced amenorrhoea at least 3 months before:
  * Age \< 56 and \< 5 years of amenorrhoea: follicle-stimulating hormone (FSH) levels to confirm postmenopausal status.
* Metastatic breast cancer (stage IV) or non-operable locally advanced breast cancer (stage IIIB).
* Positive estrogen and/or progesterone receptors as \>10% cells or \>10fmol/mg.
* Measurable disease as per Response Evaluation Criteria in Solid Tumors (RECIST) criteria.
* Patients who have received adjuvant tamoxifen are eligible, if progression has been established at least 24 months since treatment start.
* Neoadjuvant chemotherapy is allowed if progression has been established at least 12 months after end of treatment.
* Patients may have received a first line of chemotherapy for advanced disease, but treatment must have ended at least 4 weeks before enrolment, and all acute toxicities must be resolved. Previous treatment with Herceptin is allowed.
* Normal haematological, hepatic and renal functions.
* Performance status ECOG of 0, 1, 2.
* Life expectancy superior to 3 months.
* Written informed consent.

Exclusion Criteria:

* Previous hormone treatment for metastatic disease.
* Previous treatment with aromatase inhibitors.
* Inflammatory breast cancer, or aggressive metastatic disease, or visceral lesions, or metastasis in the central nervous system (CNS).
* Non-measurable disease.
* Second malignancy except for basal skin carcinoma or cervical in situ carcinoma adequately treated. If other malignancies, patient must have a disease-free period superior to 5 years.
* Treatment with any investigational product in the 4 previous weeks.
* Patients with negative estrogen and progesterone receptor tumours.