When cells are exposed to heat, the therapy stimulates the production of proteins called Heat Shock Proteins (HSP’s). These proteins play a variety of roles within the cell and immune response. HSPs can act as alert signals, activating the immune system. They are also able to refold denatured (damaged) proteins- part of the cellular repair mechanism, or mark irreversibly damaged proteins for destruction - initiating what is called apoptosis, or programmed tumor cell death. When heat specifically destroys tumor cells, the cell releases tumor antigens that can be recognized by the immune system.