Why is cancer so much more common and widespread today compared to the past?

Everybody today knows somebody who has cancer, and it is not just limited to adults anymore. Cancer rates are higher in every age group today than they have ever been. Why do you think this is? Is it from the carcinogens we are exposed to in the workplace and at home? Or, do you think it is more likely due to our diets and lack of exercise in America? Or, maybe it is that we are around so many electrical devices, such as cellular phones and microwaves? What do you think is the reason(s)?