My personal opinion on the rise of cancers in the last hundred years is simply this. We have dumped so much into the air, onto the ground, and have added so many chemicals to our food in so many ways, that it is catching up to us. So many cancers that have never been seen, birth defects that can't be explained, and health issues of all types that are skyrocketing.
Most people are drinking water that has toxic chemicals that they don't know about. It was common place for companies to take all sorts of chemicals into the hills, or backwoods of this country, and dump it on the ground, or store it in steel drums that leaked.
The odds that cast iron is the cause of the cancer issues of today is highly unlikely. We've poisoned the earth, and are now paying for it.
Some believe that CI adds iron to the diet, but we all work so hard to seal the iron with seasoning to make it shine like black glass, and make it non-stick. I tend to believe that the iron added to your diet from CI is minimal at best. I've heard discussions for both ends of this. This is JMHO, but I'm always open to discussion. I don't have a one track mind. :)