A general vaccine against cancer on the same lines as those used against influenza or other infectious diseases is not possible. This is because there are so many different forms of cancer that there can be no one single overall immunization. What is feasible, however, is inoculation against infections which increase the risk of certain types of cancer. People can now be vaccinated against carcinogenic wart viruses. These reduce the risk of liver and cervical cancer.
Another way of immunizing against cancer is with a form of immune therapy in which, after the disease has broken out, the patient's immune system can be activated to fight against the cancer cells. The aim is to try to increase the number of immune cells which are able to recognize cancer cells from their external characteristics, and then destroy them.