The National Cancer Institute says the vast majority of cancer doesn’t happen to us — it’s most often self-inflicted as 70 percent of all cancers are “lifestyle-related.” Kerry Finegan is a spokeswoman for the Iowa chapter of the American Cancer Society.Finegan says most people think most cancer is hereditary, while the fact is most cancer is preventable. Finegan says a third of all cancer is related to smoking or the use of tobacco, and another third is related to poor nutrition and inactivity.Finegan says breast, colon and prostate cancer is often related to diets that have too many fats, and too many calories. Increasing physical activity has been shown to cut your risk of developing many types of cancer by as much as half.