Biological Response to Tamoxifen (TAM) in Patients With Breast Cancer Non Metastatic RH+

Inclusion Criteria: * Adult Females (≥ 18 years), with effective contraception. The contraceptive should not use estrogen to a derivative. It must be continued during treatment with tamoxifen for at least two months after his arrest. * Histologically confirmed diagnosis of invasive breast cancer, previously untreated. Patients have been supported for a breast cancer may be included if a period of at least 2 years between the last systemic treatment of inclusion in the study. * Primary tumor hormonopositive: ER and / or PR ≥ 50% by immunohistochemistry. * Lack of HER2 overexpression * Palpable primary tumor or greater than or equal to 20 mm in diameter, measured by ultrasound * Patient scheduled to undergo breast cancer surgery * No metastases * Clinical Stage M0 * Performance index ≤ 1 (OMS) * Neutrophils WBC \> or = 1500 / mm3, Platelets \> or = 100 000/mm3 Hemoglobin ≥10 g/dL * Normal liver function: bilirubin ≤ 1.5 x ULN, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 x ULN (≤ 5 x ULN if liver metastases). * Normal renal function (creatinine ≤ 1.5 mg / dL or creatinine clearance ≥ 60 mL / min) * Cardiac function (MUGA scan or ultrasound February\> 55%) and lung function, 5.2.2 Criteria related to participation in the study: * Patient affiliated to social security, Patient has signed and dated consent Non-Inclusion Criteria: 1. Pregnant or Breastfeeding women 2. Use of St. John's Wort (herbal tea ...) within 5 days before starting treatment 3. Consumption of grapefruit juice in the last 5 days of starting treatment 4. Congenital galactosemia 5. Glucose and galactose malabsorption 6. Lactase deficiency 7. Co-medications that may interfere with cytochrome P450: 8. Ongoing Enzyme inducers: * Antiepileptic drugs: carbamazepine, phenobarbital, phenytoin * Antinfectieux: rifampin, rifabutin, névrirapine, griséofilvine, efavirenz 9. Ongoing Enzyme Inhibitors: * Inhibitors of serotonin reuptake: fluoxetine, paroxetine * Thioridazine. Quinidine * Amiodarone * Ca antagonists: diltiazem, verapamil * azole antifungals ketoconazole, fluconazole, miconazole. * No protease inhibitors: ritonavir, nelfinavir, amprenavir, indinavir. * Macrolides: erythromycin, clarithromycin, josamycin