Cancer cells present signal on their surface that causes them to be eaten by immune cells..

Research has revealed that many types of cancer cells have a protein on their surface (calreticulin) that marks the cells as targets for destruction.  The cancer cells also produce a protein that protects them from being destroyed (CD47).  Whether or not the cancer cells die seems to be based on which of the signals is stronger.  Researchers have developed an antibody that blocks the activity of CD47, opening up the possibility of a treatment that can tip the balance towards cell death.  Normal cells do not have calreticulin  on their surface so they should not be harmed by this treatment.