By acting on a patient’s own cells rather than an infectious agent, the successful trials of a new breast cancer vaccine in mice offer an important possible development in cancer treatment.

Vaccines are usually used to prevent infectious diseases. They do this by causing an immune response when introduced into the body. This basically means that the body produces white blood cells to destroy the vaccine. Then, if a genuine threat appears, say in the form of a virus, the body recognises its protein coating and is able to produce white blood cells to attack and destroy the virus more quickly, thus preventing infection.

Vaccines are therefore typically made from a dead or weakened agent such as bacteria or viruses, or from the toxins they produce. This is still true for the cancer vaccines currently available, such as that used to prevent cervical cancer – the virus causing the cancer is being targetted rather than the tumour cells themselves. However, for this process to work, the body must automatically recognise the vaccine as a potential threat, and this cannot happen with the body’s own tissue. This is a key breakthrough with the breast cancer vaccine – immune systems were trained to recognise as dangerous a particular protein that is involved in the formation of tumours. This breakthrough is even more important because the protein chosen is present in a wide range of breast cancers.

There are, of course, caveats. So far, the treatment has been shown to work only in mice. Even if it also works in people, it will not be approved for many years yet. Also, the reason that it work on breast tumours is that it targets a protein normally produced only during lactation. Apart from the fact that this means that vaccines can be used past the age when breast feeding would be needed, it also means that the process is less easy to use for other tumours. In particular another protein would need to be found that was not present in normal cells.

However, this is still a big step forward. Whilst many cancers are caused by viruses, an approach that targets the tumours themselves rather than their cause offers the hope of a more fundamental method of prevention.