While some cancer survivors are more likely to develop a new tumor than others, little is known about the complex interaction of factors that lead to this increase in risk. The chance of developing a second cancer can be affected by a variety of factors, including shared causal factors, such as lifestyle and environmental exposures, genetic susceptibility, and combinations of risk factors including gene-gene and gene-environment interactions. As more research focuses on the issues faced by cancer survivors, scientists hope to provide answers that will allow for improved therapy and care. Researchers also believe that knowledge gained from these studies will improve the quality of life for all cancer patients.