Most cancers are rare in your 20s and 30s, then get dramatically more common every year after from your mid 40s roughly.
To me, this suggests that the mechanisms that stop you getting cancer (and your body/DNA repairing in general) are themselves failing.
Of course, if everyone was 25 forever we'd still all eventually die of cancer, but it would take a lot longer than the current state of affairs.
But most people don't really want to hear that. We hear "big, scary death label disease" and we want someone to promise they can nuke it from orbit. No one wants to hear that we need to care for the body and foster its health while battling this "demon."
An immune system that has a hair trigger to new antigens would likely cause more problems than it solves. Some kind of ability to have contagious antibodies might be an actual improvement but the fact that we don't see that in nature tells me it has downsides that are difficult to see.
My biology education is a bit weak, but off the top of my head, autoimmunity being contagious sounds like a likely side-effect of contagious antibodies.
The Pfizer/BioNTech vaccine was created in hours after Covid was sequenced. So this might not be a too far fetched idea.
I think that has much less to do with the immune system, although I think that can be a factor too
It’s just probability from a flawed replication process
That and we probably need to repair the immune system. The incident of cancer increases with age, after all.