Solid organ transplantation provides life-saving treatment for end-stage organ disease but is associated with substantially elevated cancer risk, largely due to the need to maintain long-term immunosuppression. Despite previous research, important research questions remain concerning the role of immunosuppression and other factors in causing cancer in the setting. The investigators propose linking a database of U.S. transplant recipients (458,834 transplants, 1987-June 2010), donors, and wait list candidates, and to multiple U.S. cancer registries. This linkage will allow identification of incident cancers in transplant recipients. Using these data, investigators will conduct a detailed evaluation of the spectrum of cancer risk in transplant recipients. Additionally, the investigators will examine cancer risk in transplant recipients in relation to whether donors themselves had cancer, to study possible donor-to-recipient transmission of cancer. The investigators will also study whether proposed cancer risk factors (e.g., underlying medical condition, infection with oncogenic viruses, immunosuppressive medications), documented in transplant files, are associated with increased risk of particular types of cancer.