Vaccines work by previewing a foreign object, that if seen again, the immune system will attack. The big difference in treating cancer is that there is nothing

Vaccines work by previewing a foreign object, that if seen again, the immune system will attack. The big difference in treating cancer is that there is nothing 'foreign' about cancer - it arises from one's own cells. Cancer is an unproductive or even malicious mashup of material already found in the human body, very much unlike a viral or bacterial infection. There are no natural differences in kind that can be detected by an immune system that would not otherwise attack healthy tissue as well. In this case there is essentially a synthetic sensor designed and provided to the immune system that is precisely tuned in the lab to detect the (very subtle) differences between a cancer cell and a healthy cell.