Study Assessing Efficacy of ZARNESTRA™ Combined With Tamoxifen in Patients With Advanced or Metastatic Breast Cancer

Inclusion Criteria: * Histologically proven, metastatic or locally advanced inoperable breast cancer * Tumor considered potentially hormone-sensitive, i.e. presence by IHC of hormone receptors for estrogens (ER+ for more than 10% of cells) and/or progesterone (Pg+ for more than 10% of cells) or both. This expression may have been detected on the primary tumor or at a metastatic site. The method used will be reassessed by IHC if it involves a radioligand technique whenever it is possible to obtain histological material. * Progressing on treatment with tamoxifen, given either as adjuvant treatment or for advanced/metastatic breast cancer. Any previous treatment with a steroidal or nonsteroidal antiaromatase in a neo-adjuvant, adjuvant or metastatic situation is permitted. Likewise, any previous treatment with chemotherapy and/or herceptin in a nonmetastatic situation is permitted. * Post-menopausal patients * Age \> 18 years * At least one measurable lesion according to the Response Evaluation Criteria for Solid Tumors (RECIST) criteria; for patients who only have bone metastases, an evaluable non-irradiated lytic lesion is required * Performance Status (WHO): PS ≤ 2 (Appendix 1). * Laboratory tests in accordance with the following criteria: Neutrophils ≥ 2x109/l,Platelets ≥ 100x109/l,Hemoglobin ≥ 10 g/dl, ASAT, ALAT ≤ 2.5 N , or \< 5 N when liver metastasis,bilirubin ≤ 1.5 N creatinin ≤ 1.5 N * Signed, written consent before any study-related procedure Exclusion Criteria: * Men * Pre-menopausal patients who are not receiving concurrent LHRH agonist therapy * ER- and PR-negative patients * Contraindication to antiestrogens (thromboembolic risk) or ZARNESTRA * Non metastatic tumor susceptible to management by radiotherapeutic and/or surgical means * T4d inflammatory tumor (PEV 2 or 3). * Short-term, life-threatening lesions: hepatic invasion \> 1/3 of liver volume, pulmonary lymphangitis, uncontrolled cerebral metastases, carcinomatous meningitis * Sensory neuropathy \> or = grade 1 (WHO) * Previous history of uncontrolled cancers or controlled for less than 5 years, except basal cell skin cancers and in situ cancers of the cervix. * Chronic diseases (somatic or psychiatric) with a poor prognosis * subjects with enzyme-inducing anti-convulsants (e.g., phenytoin, phenobarbital, carbamazepine) : this treatment is not permitted while taking ZARNESTRA * Patients who, for family, social, geographic or psychological reasons, could not be followed up correctly.