The biological response to treatment with tamoxifen in the preoperative situation is studying in this protocol. This study will enrolls patients with non-metastatic breast cancer HR +.

The relationship between the CYP2D6 polymorphism, pharmacokinetics and biological efficacy of TAM will be studied.

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