Consider that a lot of skin cancer is caused by the sun, which has been around longer than humans have been on Earth.

But rates of cancer have skyrocketed in the past century, partially due to more man-made carcinogens, but mostly due to the fact that people live much longer nowadays, giving them much more time for cancer cells to form.

Before the 1900's, many people died of malnutrition and infections and injuries - which are all managed much better with modern medicine - so very few people back then lived long enough to have cancer.