To assess the contributions of mitochondrial and non-mitochondrial p66ShcA pools on breast cancer growth and metastasis, we re-expressed versions of p66ShcA that can [p66-CR (WT)] or cannot [p66-CR (S36A)] generate mitochondrial ROS in p66-null [p66-CR (VC)] lung-metastatic breast cancer cells. The gene discussed is SHC1; the disease is breast cancer.