Breast cancer is the most common cancer affecting women in England and Wales, with about 40,500 new cases diagnosed and 10,900 deaths recorded in England and Wales each year. In men breast cancer is rare, with about 260 cases diagnosed and 68 deaths in England and Wales each year (Office for National Statistics, Cancer statistics registrations: registrations of cancer diagnosed in 2005, England; Welsh Cancer Intelligence and Surveillance Unit, Cancer incidence in Wales 1992−2002). Of these new cases in women and men, a small proportion is diagnosed in the advanced stages, when the tumour has spread significantly within the breast or to other organs of the body. In addition, there are a significant number of women who have been previously treated with curative intent who subsequently develop either a local recurrence or metastases. Over recent years there have been important developments in the investigation and management of patients with advanced breast cancer, including new chemotherapy, and biological and hormonal agents. There is some evidence of practice variation across the country and of patchy availability of certain treatments and procedures. This clinical guideline helps to address these issues and offers guidance on best practice.