What we want is prevention, not early detection. Bear in mind that prevention is a proven outcome, because some people never get Alzheimers, and some people never get cancer. Detecting cancer or Alzheimers early and then intervening to cure the condition is actually not something that is definitely possible.
Even taking your example, getting to the point of removing a pre-invasive adenocarcinoma is actually very complicated. You need a motivated patient, you need a healthcare team of specialist doctors or nurse practitioners, pathologists, radiologists, anaesthesiologists, nurses, an endoscopy suite, a recovery area, you need a system to follow up and track these cases etc. The full embedded cost of this undertaking is huge, I don't think it is scalable, and at the same time, will never capture everyone. Randomised studies usually just barely show that these screening approaches are better than not screening, once false positives are accounted for. Furthermore, you have chosen an example where there is a useful pre-screening test (fecal blood tests), a relatively non-invasive diagnostic test (colonoscopy) and a relatively painless intervention (removing a polyp with the scope). This is not broadly applicable. A pancreatic lesion for example is very hard to diagnose for sure, and the intervention is a massive and life changing operation.
Cancer prevention is best, I agree, but it's not always clear that it can be perfectly prevented. So then you have to move to detection and therapeutic intervention to either eliminate the cancer or prevent it from materially impacting the health of the individual. And with cancer specifically, early detection is one of the best predictors of a good outcome. This is not always possible of course, some cancers are very difficult to detect, but some aren't. It just seems like we are making perfect the enemy of good.
The strongest argument is an economic one. If we can develop preventative treatments that we can just give to everyone, it is a much more justifiable expenditure. The risks and benefits are much clearer. This is in contrast to what we do now, which is apply extremely expensive and complex care to a group of people that are diagnosed with cancer. There are only a small number of people in the world that can even get this care. Consider that a preventative therapy is the only type of therapy some people in the world will ever get for their cancer. Papua New Guinea for example has zero oncology specialists in a country of 8 million people.
In case it didn't come through I'm 100% agreement with you on this. Learning about TIL and CAR-T therapies now, but in general feel that cancer vaccines would rival any pharmaceutical on the market in terms of profitability and net decrease in global misery.
Just trying to optimize the time between now and that (IMHO) inevitable day.
1. Even the best tests have a chance that the scan will produce a false positive. If we indiscriminately test everyone for every disease under the sun, most of the findings will be false positives.
2. The benefit must outweigh the cost of the test. Both in terms of expense, and intrinsic factors such as radiation exposure.
3. Certain things that show up in a scan would never cause a problem if they were just left alone. In these cases detecting it early has little benefit, and may lead to unnecessary interventions.
4. If a cure is not available, testing for the disease may not always be appropriate, from an ethics point of view.
You can always choose not to act on what you learn. You can't act on what you don't know.
You can also act on what you think you know but in fact don't. False negatives kill people but so can false positives.
There is presently some set of screening tests with varying levels of sensitivity and specificity, and they aren't all appropriate for mass screening. However, if millions of people started regularly getting non-ionizing imaging done through MRI or ultrasound or infrared or whatever, we would learn a shitload about predicting maladies and likely save quite a few more people than we kill in the process.
I couldn't say, but I wage the medical science community / industry is cognizant of the phenomena and, not being an expert in the field myself, I trust them to handle the matter reasonably. In the specific case of breast cancer, I've heard that the cost of false positives is high enough to be a major consideration in recommended breast cancer screening schedules.