Despite several significant advances in the treatment of breast cancer in the last decade, breast cancer remains a potentially life threatening cancer.In the United Kingdom up to 12000 women die per year from metastatic breast cancer.The majority of these patients will have received radiotherapy and chemotherapy as part of their treatment.Primary or acquired resistance to such therapies is the usual cause of such treatment failure.The mechanisms by which breast cancer cells are ill understood.Traditional methods of investigating drug resistance have or evaluation of single proteins of particular interest.However, resistance is probably multifactorial and such an approach will not capture all the mechanisms involved.