The current thought is that cancer arises by tissue stem cells accumulating mutations at a low rate until it goes out of control. Every division there is some chance of error. If you have more divisions, there is a higher chance of cancer.
If you always keep this in mind: cell division -> cancer, so much will make sense. Anything requiring an increase in cell division will increase the chances of cancer in that tissue (smoking damages lung cells which need to be replaced, uv damages skin cells, being larger means you have more cells).
That is not to say that immune surveillance for clearing these bad cells plays no role, or that DNA damage sensitivity/repair can't be increased/decreased, or that those rates need be similar in different species. However, the main idea behind the entire modern cancer research programme is that cell division -> cancer.
"If you always keep this in mind: cell division -> cancer, so much will make sense."
I am not so sure this is a good heuristic.
An athlete, or even a moderately active (fit) person is inducing quite a bit of cell division due to the teardown and regrowth of muscle and bone, etc., caused by exercise.
However, activity and exercise seem to be (strongly) negatively correlated with cancer.
Instead, I think a better mental model is the winnowing of a population. When you subject your (muscles/bones/heart/lungs) to a highly stressful exertion, some of the cells just can't maintain that output and so they are killed off, or commit suicide by the process of apoptosis.
But if you never subject your cell population to an apoptosis-inducing level of stress, you're just cultivating an increasingly weak population of cells.
I highly recommend the book by Nick Lane titled: Power, Sex, Suicide which explores these topics...
The current thought is that cancer arises by tissue stem cells accumulating mutations at a low rate until it goes out of control. Every division there is some chance of error. If you have more divisions, there is a higher chance of cancer.
If you always keep this in mind: cell division -> cancer, so much will make sense. Anything requiring an increase in cell division will increase the chances of cancer in that tissue (smoking damages lung cells which need to be replaced, uv damages skin cells, being larger means you have more cells).
That is not to say that immune surveillance for clearing these bad cells plays no role, or that DNA damage sensitivity/repair can't be increased/decreased, or that those rates need be similar in different species. However, the main idea behind the entire modern cancer research programme is that cell division -> cancer.
More info: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC54830/