Cancer cell death. Artwork of killer T-lymphocyte white blood cells attacking cancer cells (dull red). A cancer cell is bursting as it undergoes Programmed Cell Death (PCD or apoptosis), which has been induced by chemicals released by the lymphocyte cells. Killer T-lymphocytes are part of the body's immune response system. They are programmed to seek out, attach themselves to and kill cancer cells. They recognize cancer cells by the unusual chemicals (antigens) on the surface of those cells.