It's not recommended to get what are called full body scans - one of the main reasons is all the false positives and unnecessary alarms it causes. Most of us have some artifacts that will show up on various scans and will look exactly the same next year and next decade.

On the other hand, many tumors are now discovered incidentally when getting a scan for something else. That tends to also cause higher anxiety levels, but at the same time allows addressing a real issue at a much earlier stage.

Some cancer screening (such as for prostate) is generally done through blood test. Colorectal cancer screening has the "benefit" of the doctor being able to get a front-row-center view. And some are detected by mri or even straight-up x-ray. There all quite different, as is the expertise needed for diagnosis.