The term cancer vaccine is often used to describe a process whereby a person's immune system is coaxed into recognizing and destroying malignant cells without harming normal cells. A cancer vaccine is generally considered an immunotherapy, because, unlike prophylactic vaccines against diseases such as polio, influenza, and tuberculosis, a cancer vaccine is not preventive and must be administered after cancerous cells develop.

Problems

A vaccine against a particular virus is relatively easy to create. There are usually only a few viable variants of the virus in question. It is very hard to develop vaccines for viruses that mutate constantly such as influenza or the HIV virus.

A tumour can have many different types of cells in it, each with different cell-surface antigens. Furthermore, there are many different types of cancer, separated by anatomical location, cell histology, aggressiveness etc. The development of a vaccine to address all these possibilities is a formidable task, and impossible with current technology and funding. Future advances in the understanding of cancer genetics and gene therapy may make it possible to vaccinate against certain common cancers, such as prostate cancer.