Where do cancer risk statistics come from?

Most information about cancer risk and risk factors comes from studies that focus on large, well-defined groups of people. Cancer researchers have identified many of the major environmental factors that contribute to cancer, including smoking for lung cancer and sunlight for skin cancer. Uncovering more subtle cancer risks has proved more difficult.

Many studies of cancer risk factors rely on observational approaches. In these studies, researchers keep track of a group of people for several years without trying to change their lives or provide special treatment. This can help scientists find out who develops a disease, what those people have in common, and how they differ from those who didn't get sick.