Objective response to treatment as a potential surrogate marker of survival in breast cancer

Until recently, objective tumor response to chemotherapy was used as the primary endpoint in phase II trials aimed at assessing the anti-tumor activity of new drugs. However, it was not accepted as a surrogate endpoint of survival for efficacy trials in solid tumors, and it was not believed to be associated with survival benefit. The recent demonstration that objective response is indeed a valid surrogate endpoint of survival in colorectal cancer, together with strong indirect evidence supporting a similar role of response in breast cancer, opens new possibilities for both the design of trials in metastatic breast cancer and the clinical decision in individual patients with the disease.