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one more thang.
I read somewhere else (several places)
that we get hundreds of cancers (regularly)
but our immune system kills them (mostly)

Our immune system can sometimes recognise cancer cells and kill them as long as they don't overgrow in numbers. Our DNA replication enzymes actually make thousands of mistakes per day but we have correcting mechanisms. One of these is what we call Tumour Suppressor Genes. They detect faulty and potentially cancerous DNA and they prevent the cells having that DNA from multiplying. But sometimes the mutations caused by damaged DNA will deactivate the Tumour Suppressor Genes and allow for the uncontrolled growth of cancerous cells.

I'll look more into it. Genetics is an area that I'm really interested in. Thanks for your comment!