In patients who have undergone organ transplantation, understanding causal links between exposures (risk factors), such as immunosuppression and outcomes (disease states), such as certain cancers, is vitally important for prevention, treatment, and optimization of transplantation. The fields of epidemiology and biostatistics utilize different study designs, including descriptive analyses and exposure/outcome studies, (such as randomized trials, cohort studies, and case-control studies) for such analyses. All studies, regardless of design, rely on data. Although randomized trials involve prospective monitoring of two or more groups over time, most of our knowledge regarding disease causation comes from studies of retrospectively collected data. As such, one of the most powerful epidemiologic tools is found in the formation and continuation of well-designed databases.

In 1971, the U.S. congress passed the National Cancer Act. This act mandated physicians and hospitals to collect and publish data for the treatment and prevention of cancer. Since that time, further laws have been established for mandatory reporting of cancer incidence and data to a centralized national registry through the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute (NCI). SEER currently collects and publishes cancer incidence and survival data from population-based cancer registries covering approximately 26% of the U.S. population. Specific to organ transplant recipients (OTRs), the United Network of Organ Sharing (UNOS) is the organization that administers the nation's Organ Procurement and Transplantation Network (OPTN) and maintains the largest database and cancer registry for solid OTRs in the United States.