Although breast cancer is one of the leading killers of Canadian women, the molecular basis for the events involved in breast cancer initiation and progression remain poorly understood. To address this important problem, we will employ state of the art transgenic mouse models and conditional knock-out models to assess the relative contribution of particular signaling molecules to each stage of breast cancer progression. Given the prevalence of breast cancer in human populations, our research program will provide important insight into molecular basis of these poorly understood human diseases.