The bad news is that there are lots of persistent chemicals in our environment which are hardly broken down at all by biological activity. Some of the chemicals are mimics of human hormones like estrogen that are associated with causing cancer. Chemicals like these have been accumulating in animals and have even been found in polar bears in the arctic. Whether this aspect of our environment will be leading to an eventual increase in cancer remains to be seen. Cancer is starting to decrease with some exceptions.
Epidemiology shows some potential causes of cancer.
Much cancer is probably caused by environmental carcinogens.