A. Incidence of most cancers increases with age in a very uniform way.
Cancer is caused by random(ish) mutations creating cellular variants that have uncontrolled growth - typically you need multiple mutations. It's related to age mostly because you accumulate mutations over time - it's a game of chance.
So the underlying cause is the same - mutations - however there are lots and lots of different ways to mutate a cell into a dangerous state ( that's not to say there are not common mutations found across lots of cancers in key regulatory targets ).
Different species effects
I don't think this is well understood, but some of that is to do differentials in effective DNA repair or detection of cancer cells by the immune system ( you body can detect and kill cancer cells as if they were foreign invaders ).
The other thing is perhaps less exposure to mutation causing agents ( humans are probablyt exposured to lots of mutagenic things at a low level we don't really know about yet - scandals of the future ) - and birds not getting cancer is probably mostly they don't live long enough.
And finally if your cancer get's to a later stage - typically it just hasn't picked up mutations to grow faster it's probably picked up mutations allow it to evolve faster ( ie a higher mutation rate ) - they means a single cancer that started from a single cell can evolve into a tree of related cells with different sets of mutations. ) And it's those different mutations that allow cells to survive in parts of the body they weren't originally from ).
In terms of treatment of cancer you need to try and target a difference between normal and cancer cells - so you tend to go after those differences driven by the mutations - often making the treatments sub-type specific. ie this particular cancer is different from normal in this way - so we target that difference, others might be different in another.
There are some treatments that are more generic - chemo basically targets fast growing cells ( for whatever underlying reasons ) - however these don't differentiate between normal fast growing cells and cancer so they have quite nasty side effects.
Comments
Cancer is caused by random(ish) mutations creating cellular variants that have uncontrolled growth - typically you need multiple mutations. It's related to age mostly because you accumulate mutations over time - it's a game of chance. So the underlying cause is the same - mutations - however there are lots and lots of different ways to mutate a cell into a dangerous state ( that's not to say there are not common mutations found across lots of cancers in key regulatory targets ).
I don't think this is well understood, but some of that is to do differentials in effective DNA repair or detection of cancer cells by the immune system ( you body can detect and kill cancer cells as if they were foreign invaders ). The other thing is perhaps less exposure to mutation causing agents ( humans are probablyt exposured to lots of mutagenic things at a low level we don't really know about yet - scandals of the future ) - and birds not getting cancer is probably mostly they don't live long enough.
And finally if your cancer get's to a later stage - typically it just hasn't picked up mutations to grow faster it's probably picked up mutations allow it to evolve faster ( ie a higher mutation rate ) - they means a single cancer that started from a single cell can evolve into a tree of related cells with different sets of mutations. ) And it's those different mutations that allow cells to survive in parts of the body they weren't originally from ).
In terms of treatment of cancer you need to try and target a difference between normal and cancer cells - so you tend to go after those differences driven by the mutations - often making the treatments sub-type specific. ie this particular cancer is different from normal in this way - so we target that difference, others might be different in another.
There are some treatments that are more generic - chemo basically targets fast growing cells ( for whatever underlying reasons ) - however these don't differentiate between normal fast growing cells and cancer so they have quite nasty side effects.