One of a group of proteins that help protect cells from stresses such as heat, cold, and low amounts of oxygen or glucose (sugar). Stress proteins help other proteins function in normal cells and may be present at high levels in cancer cells. Blocking the activity of a stress protein called HSP90 is being studied in the treatment of cancer. Other stress proteins including HSP70 and gp96 are being studied in vaccines to treat cancer. Also called heat-shock protein and HSP.