The immune system protects the body from attacks by pathogenic microorganisms (such as viruses and bacteria) and by cancer cells. Tumors often contain a large number of immune cells which have an inherent capability to attack the cancer cells. However, cancer cells usually evade the immune system, for example by producing immunosuppressive substances. With immunotherapy, the ability of the immune system to fight cancer cells is improved in an effective manner, and the defense mechanisms used by the tumor are blocked or weakened. In addition, immune cells capable of destroying the cancer cells will survive in the body and thus protect it from metastases that may arise after treatment has ended. This “vaccination effect” is unique for immunotherapy.