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).