[Expez]

> Scientists also developed a way of "carbon dating" mutations. They showed that more than a fifth of them occurred years or even decades before a cancer is found.

> He added: "Unlocking these patterns means it should now be possible to develop new diagnostic tests, that pick up signs of cancer much earlier."

The journalist probably pressed this last point, because it can't possibly be true in a practical sense. Even if you can detect these changes early on in cells, we can't possibly test every cell in the body for mutations on e.g. a yearly basis, right?

[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.

[jarrad2000]

Even if you could, it does not help if there isn't a good treatment.

That's why screening for some cancers (e.g. breast and prostate) is controversial.

First of all you might get false positives or negatives. False positives can harm patients since they get worried and might even get treatment for a disease they don't have.

Secondly even if the screening gives a valid result: In some cases (like mentioned before PC and BC) that does not mean the patients live any longer than the ones who where not screened.

There's a 5-year survival time metric which makes screening look very positive.

Let's say you and a friend have a cancer that will kill you in 10 years, no matter what. If you get screened after 4 years, you'll have a 100% 5-year surivival rate (so screening is celebrated as a success: more screening!).

However, you won't live a second longer than your friend. You will be worried though and might get treatment with serious side effects.

That's why the mortality rate is IMO an actually much more interesting metric.