Background: Due to improvements in early detection, supportive care, and treatment, the number of cancer survivors in the United States has tripled since 1971 and is growing by 2% each year. In 2001, there were f10 million cancer survivors, representing 3.5% of the population. As survival after a diagnosis of cancer improves, quantification of the late effects of cancer and its therapy become critical. One of the most serious events experienced by cancer survivors is the diagnosis of a new cancer. Second-or higher-order cancers now account for f16% of incident cancers reported to the National Cancer Institute's Surveillance, Epidemiology, and End Results Program. Subsequent neoplasms may not necessarily be attributable to prior cancer treatment but may also reflect the effect of shared etiologic factors, environmental exposures, host characteristics, and combinations of influences, including gene-environment and gene-gene interactions.