6ABC reports that the American Cancer Society is making a last push to enroll people in a study that will help figure out what causes cancer and how we can better prevent it. It's called the Cancer Prevention Study Number Three, or CPS-3. Studies like it in the past have linked smoking and obesity to cancer and, today, that's how we know those are risk factors. Carmen Guerra, MD, associate professor of Medicine and a volunteer with the American Cancer Society, says the study is one-of-a-kind. It will follow people over the course of 20 to 30 years and pinpoint risk factors - such as genetics, lifestyle and environment - that can lead to cancer. "This study will really help us identify so much of what we still don't know about what causes cancer and, if we can do that, we could save lives, we could prevent another family from hearing 'You have cancer,'" she said.