[DrScientist]

Correct. And even if you could, you would find everybody has some of these potentially dangerous mutations somewhere.

The problem only comes if get the right combination in a single cell and then the cells starts to multiply.

At that stage you might then be able to pick up evidence from circulating tumor DNA ( https://ghr.nlm.nih.gov/primer/testing/circulatingtumordna ) from a blood test.

[allovernow]

We'll hold on now. If we assume that mutations tend to cluster around cells exposed to particular carcinogens, and assume there is some number N>≈5 mutations required, in theory we could look for cases where many cells present with x% of the necessary mutations. And it becomes much easier to detect because you presumably have many cells which mutate stochastically together.

[DrScientist]

You are describing a cervical smear test - target cells more likely to be mutated - assume that if you find problem cells in your test ( after you have destroyed during the test ) that there are similar ones still left in the body ( not because they were mutated together - but because they are related - one cell inherited a mutation from another ).

So sure. That's done already and having a test which detects 'precancerous' based on genetics might be useful. One of the problems at the moment is the treatment is often almost as bad as the cure - so you might only be able to step up frequency of the tests.

The problem with this approach is only certain bits of the body are easily accessible in this way - that's why people like the ctDNA tests - but they have their own challenges.

Another non-destructive way would be imaging - either thermal ( cancer cells are more active and so hotter than normal ), or using some sort of labelling markers - however can't see a way to target arbitrary early genetic mutations with this.