> Eg that unless something is obviously wrong you wouldn’t action based on any findings from a full body scan; instead you would retain the record and repeat the scan 12-24 months later. Compare anything notable for growth or other irregular change, rinse and repeat. I would imagine that would greatly decrease the amount of pointless imaging and biopsy done. There would certainly still be some done but is that not the case now?

The problem is birds vs rabbits vs turtles (I didn't invent this; it's a classic metaphor [1]).

For any given finding on an MRI, they're going to be, tautologically, in one of three categories, in descending order of frequency:

* turtles (i.e. slow growth tumors). Most people of a certain age have them, and they'll never be an issue. MRIs will find them. You can't know they're turtles.

* rabbits (faster-growth, non-metastasized tumors). Maybe we can catch these, because they're slower than birds, and maybe can make a difference. Everyone wants to believe they're finding rabbits, but just because of the nature of the distribution, they're most likely finding turtles.

* birds (i.e. fast metastasizing tumors; think days or weeks). This is what you want to catch, because they're metastasizing. They're deadly. They're rare. You'd like to catch these before they fly away, but how often are you going to run an MRI? Daily?

Asymptomatic screening almost always catches turtles, sometimes catches rabbits, and rarely catches birds. You can't tell the difference from a single scan...so when do you choose to go further? At what cost?

[1] https://lactobacto.com/2018/02/13/viewing-cancers-as-birds-r...

[1] https://www.northcoastjournal.com/humboldt/cancer-part-2-tur...

[1] https://www.thedailybeast.com/all-these-cancer-screenings-pr...

I included that third link -- even though it's from the Daily Beast -- because it really drives home the practical implications of the metaphor. Consider this:

> In 2012, Archie Bleyer and Gilbert Welch published a study in the New England Journal of Medicine titled, “Effect of Three Decades of Screening Mammography on Breast-Cancer Incidence.” They found that, with the advent of screening mammographies, the incidence of breast cancer in the U.S. had doubled. For every 100,000 women screened, the number of women diagnosed with breast cancer had increased from 112 to 234. At the same time, the number of women presenting with late-stage breast cancer (the kind that often results in death), decreased from 102 to 94 (per 100,000). In other words, only eight of the 122 women diagnosed with breast cancer appeared to benefit from the screening. Eight. The others had been treated with mastectomy, radiation therapy, and chemotherapy without clear benefit.

This is a common story in the world of cancer diagnostics.