This study is being carried out to see if ZD1839 is effective in treating metastatic breast cancer in combination with Nolvadex, and if so, how it compares with Nolvadex alone.

Inclusion Criteria:

• Histologically confirmed metastatic adenocarcinoma of the breast (seeTNM staging Appendix I) that is ER and/or PR positive as determined in local laboratories at each investigator site (central verification of ER status will be performed after the patient starts treatment
• A tissue block from either the metastatic or primary tumor site is required.
• WHO performance status (PS) 0-2
• Patients must not be pregnant or breast-feeding. A negative pregnancy test is required within 7 days prior to randomization if pre- or peri-menopausal. Postmenopausal patients are defined as:
• natural menopause with last menses > 1 year ago,
• radiation induced oophorectomy with last menses > 1 year ago,
• chemotherapy induced menopause with 1 year interval since last menses, or
• serum FSH and LH and plasma estradiol levels in the postmenopausal range for the institution.
• bilateral oophorectomy

Exclusion Criteria:

• Patients cannot be on hormone replacement therapy or received prior chemotherapy for metastatic disease.
• Patients previously treated with a Tyrosine Kinase inhibitor or have evidence of an active interstitial lung disease are not eligible.
• Treatment with LH-RH analog.
• Laboratory values as follow Bilirubin >1.5 times upper limit of normal ULN, alanine amino transferase (ALT) or aspartate amino transferase (AST) >2.5 times the ULN if no demonstrable liver metastases, or >5 times the ULN in the presence of liver metastases
• Bone marrow function: WBC <1500 mm3