Here is a thought provoking article that suggests that cancer rates were far lower in antiquity. The study points to low rate of incidence in Egyptian Mummies (less than 1 in 100) as compared to modern prevalence (one in 8 deaths).
One worthwhile point the article linked above references is that cancer was around before humans and therefore cannot be said to be fully the consequence of man-made environmental changes.
However, that study doesn’t preclude the idea that cancer is a often or almost always a result of environmental effects on cell reproduction.
Together, the two points raise the distinction of the existence of cancer versus the prevalence of cancer. Take the following questions:
1) Does cancer exist in non-human primates?
2) How common is cancer in non-human primates?
If cancer in non-human primates is far lower than in humans, it’s worth asking why. Additional clarifications can be made:
3) Do cancer rates increase for non-human primates in captivity versus a natural habitat?
4) Is the full explanation about cancer rate disparity to be located in age?
5) How much of the disparity in cancer rates between primates has to do with the presence of negative environmental factors?