Long-Term Follow-up of People Undergoing Hematopoietic Stem Cell Transplantation

Background: * Patients who survive more than 3 years after allogeneic hematopoietic stem cell transplantation (HCT) have a high probability of being cured from their underlying disease; however, mortality rates remain 4 to 9-fold higher than the general population for at least 30 years after HCT. * The most common causes of late mortality in HCT survivors include second malignancies, relapsed/recurrent disease, infections, chronic graft-versus-host disease (GVHD), respiratory diseases, and cardiovascular diseases. * Guidelines for recommended screening and preventive practices for long-term survivors after HCT have been developed, and can be implemented to detect or prevent late complications after HCT. * Understanding the pattern of immune reconstitution and immune dysregulation after HCT may help to elucidate the root mechanisms of late complications. Objective: -To collect clinical data on patients and late complications after HCT Eligibility: * Patients who underwent HCT for any indication and are surviving one year or more from the date of HCT * Related stem cell donors of patients meeting the above criteria who participated or will be participating as a donor of stem cells or leukocytes. * Age \>= 4 years * Any active disease relapse or new hematologic malignancy including post-transplant lymphoproliferative disorder (PTLD) are excluded from protocol enrollment. Design: * Prospective, longitudinal study of the natural history of long-term survivors after HCT. * Clinical data on post-transplant complications and peripheral blood samples will be collected at yearly evaluations by the Principal Investigator, LAI, AI or representative investigator of the original HCT protocol. * If patient develops complications such as new cancers, relapsed disease, new hematologic malignancy or PTLD they are exempt from required evaluations, and followed for survival and causes of death (management of complications as per primary team). * As this is a longitudinal registry study without any planned intervention, there is no formal statistical analysis plan or accrual goal; descriptive data will be reported.