The purpose of this study is to assess the efficacy of ZD6474 in patients with metastatic breast cancer at 2 dose levels.

Inclusion Criteria:

• Histological and/or cytological confirmation of metastatic breast cancer which is refractory to anthracycline, taxane, with or without capecitabine therapies;
• WHO performance status 0, 1 or 2 on the day of registration;
• Females, aged >= 18 years;
• No Gastrointestinal pathology which could affect the bioavailability of ZD6474.

Exclusion Criteria:

• Any evidence of severe or uncontrolled systemic diseases including known cases of Hepatitis B or C or human immunodeficiency virus (HIV).
• Significant cardiac event (including symptomatic heart failure or unstable angina) within 3 months of entry or any cardiac disease that in the opinion of the investigator increases risk for ventricular arrhythmia;
• History of clinically significant cardiac arrhythmia (multifocal PVCs, bigeminy, trigeminy, ventricular tachycardia), which is symptomatic or requires treatment (CTC grade 3) or asymptomatic sustained ventricular tachycardia;
• Chronic atrial fibrillation;
• Previous history of QT / QTc prolongation with other medication;
• Congenital long QT syndrome;
• Systemic anti-cancer therapy or other investigational agent within the last 4 weeks (6 weeks for nitrosoureas, mitomycin C, or suramin);
• Currently receiving drugs with known significant 3A4 inhibitory (ie, ketoconazole, itraconazole, troleandomycin, erythromycin, diltiazem, verapamil) or stimulatory (ie, phenytoin, carbamazepine, barbiturates, rifampicin) effects;
• Currently receiving therapeutic doses of warfarin (Coumadin?)