planned to design a prospective study

Primary objectives of this study is to evaluate the effects of CYP2D6 genotypes on time to progression after tamoxifen treatment in pre- or postmenopausal women with metastatic breast cancer. Furthermore, we will evaluate the effects of CYP2D6 genotypes on clinical benefit and response duration to tamoxifen administration in pre- or postmenopausal women with metastatic breast cancer and also evaluate the effects of CYP2D6 genotypes on the steady state plasma concentration of tamoxifen and its metabolites

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).