A constituent of the pepper Piper longum L. that selectively kills cancer cells but not normal cells. Piperlongumine increases the level of reactive oxygen species (ROS) and apoptotic cell death in both cancer cells and normal cells engineered to have a cancer genotype, irrespective of p53 status, but it has little effect on either rapidly or slowly dividing primary normal cells. Also potently inhibits the growth of spontaneously formed malignant breast tumors and their associated metastases in mice.