Evaluation of the Association Between CYP2D6 Genetic Polymorphisms and the Treatment Effect of Tamoxifen

Inclusion Criteria: * Histologically or cytologically diagnosed stage IV or recurrent breast cancer patients according to American Joint Committee on Cancer (AJCC) * Positive estrogen receptor or Positive progesterone receptor. * Females at least 18 years of age. * Prior radiation therapy is allowed as long as the irradiated area is not the only source of measurable disease * Prior hormone therapy less than 2. * No history of Megace medication for recent 28 days * Performance status of 0, 1 and 2 on the ECOG criteria * Clinically measurable disease, defined as bidimensionally measurable lesions with clearly defined margins on x-ray, CT scan, MRI or physical examination. Lesions serving as measurable disease must be at east 1 cm by 1 cm, as defined by x-ray, CT scan, MRI, or physical examination * Bone only or pleural fluid only disease is included as long as evaluation for clinical benefit is possible * Estimated life expectancy of at least 12 weeks * Compliant patient who can be followed-up adequately. * Adequate hematologic (WBC count 3,000/mm3, platelet count 100,000/mm3), hepatic (bilirubin level 1.8 mg/dL, AST, ALT 1.5xULN, albumin 2.5 g/dL), and renal (creatinine concentration 1.5 mg/dL) function. * Informed consent from patient or patient's relative * Childbearing women should use non-hormonal contraceptive method Exclusion Criteria: * Active or uncontrolled infection. * Second primary malignancy (except in situ carcinoma of the cervix or adequately treated basal cell carcinoma of the skin or prior malignancy treated more than 5 years ago without recurrence).