The argument for better screening would require that finding those asymptomatic cancers actually improves survival rates. There are several reasonable scenarios where early screening doesn't improve it:
* The cancer is aggressive and resistant to treatment. Chemo/radiation only pause the growth for a bit, but ultimately the cancer keeps growing and the total survival time is the same (only that the patient spent more time knowing they had cancer).
* The cancer is susceptible enough to treatment that it's still curable when it becomes symptomatic and found through other means.
* The cancer is slow enough that the patient dies from other causes before.
Early screening brings benefits only when the cancer ends up causing issues and responds differently to treatment between the "early screening detection" time and the "normal detection" time.
It's impossible to know beforehand which of the scenarios have more weight, specially because we have very little data on what happens way before cancer is detected via the usual methods. We need better studies on this, and for now the evidence doesn't really point out to these large, indiscriminate screenings being actually helpful.
* The cancer is aggressive and resistant to treatment. Chemo/radiation only pause the growth for a bit, but ultimately the cancer keeps growing and the total survival time is the same (only that the patient spent more time knowing they had cancer).
* The cancer is susceptible enough to treatment that it's still curable when it becomes symptomatic and found through other means.
* The cancer is slow enough that the patient dies from other causes before.
Early screening brings benefits only when the cancer ends up causing issues and responds differently to treatment between the "early screening detection" time and the "normal detection" time.
It's impossible to know beforehand which of the scenarios have more weight, specially because we have very little data on what happens way before cancer is detected via the usual methods. We need better studies on this, and for now the evidence doesn't really point out to these large, indiscriminate screenings being actually helpful.