Safety tests on three people, published in the journal Science, showed the immune system could be trained to fight skin cancers.

The American team said the early results marked a “significant step” towards personalised cancer vaccines.

The charity Cancer Research UK called the tests an “exciting but very early-stage trial”.

UV light can transform healthy skin cells into deadly melanomas by damaging the DNA.

The tumours are a genetic mess, containing hundreds of random mutations that are different in every patient.