Should also point out that tests will negatively affect your life seriously either way, especially if these benign cancers are common. Think of the time spent going to/from the doctor, the incredible stress (am I dying?), the tests itself: it is damaging the person's life. Detection is good, false positives are unacceptable though.
e.g.,
My two friends who got early screening had a few false positives, and one true positive treated early. One later died of heart attack and one lived long enough to get dementia.
My two friends who didn't get early screening, one died of heart attack and one died of cancer that could have been caught. Both died earlier than two above.
Sadly, at this point, you want to die of cancer, but you want to do it when you're 85. It beats a sudden heart attack and it beats dementia. You just want to prolong the outcome.
I don't know any "did early detection which lead to unnecessary chemo" stories..
I know people who died due to the lack of early detection.
I also know people who survived due to accidental pre-symptomatic detection because of unrelated ER scans where they'd have been in stage 4 before having any symptoms.
So more screenings for more types of cancer are absolutely needed. It's more treatable early, and you will have better outcomes.
Patients might worry about lab results is not a good reason not to have early detection. Patients can self select if they are so sensitive.
Nobody would give chemo if the tumor is known to benign, after all.
An unnecessary chemo will be one where they couldn't tell, and the chemo ensures they wont tell.
The only way you'll know is from aggregate mortality statistics not budging.
The other aspect is that even if a tumour isn't, earlier detection is often not reducing mortality any more once you get to a decent baseline.
The evidence often does not support early screening in general. Early screening for specific subsets of the population have better results, but are also not unambiguously helpful.
I have seen a few people get benefits from a cancer scare: a refocus onto what matters in their lives. Agree: I would guess most people just get costs. Of my middle-aged friends with health scares only a few addressed the underlying cause (and even fewer are proactively avoiding health issues).