So since Chris was hearing my footsteps ...
I actually don't think cancers are really on the rise. I think if you add up all the cancers and do an average they're probably at the same rate they've always been, just different proportions, as others have said, it's a reporting thing.
I do think autoimmune disorders are on the rise and hitting increasingly younger people. I also think food allergies and intolerances are increasing. I know endocrine disorders are going up, but there's the whole diabetes related obesity thing. Now, is the increase in obesity related purely to our shitty diets and lifestyles, maybe, maybe not.
I will always believe the vast, vast majority of disease is caused by some combination of the following (in no particular order): Stress, food additives, environmental chemical exposure (including OTC drugs, alcohol, cigarettes, prescriptions, bug spray, cologne, etc., etc., etc.), general bad diet, lack of exercise, depression, systemic yeast overgrowth, uncorrected spinal subluxations, repeated exposure to an undiagnosed food intolerance/allergy (e.g., you are actually intolerant of wheat, the main symptom is it gives you really bad heartburn.
Instead of testing you for food allergies/intolerances your doctor puts you on a proton pump inhibitor and you keep eating wheat; 30 years later you get colon cancer).
I will always believe in the body's innate ability to be healthy and maintain homeostasis given the proper circumstances.