Background: People who have had an allogeneic hematopoietic stem cell transplant (HCT) have bone marrow or an immune system that is damaged. They get stem cells from a donor who is a relative. Researchers want to study stem cell donors and recipients to learn about the long-term effects of HCT. They want to learn how the stem cells change and how to improve their ability to fight cancer.

Objective: To provide long-term follow-up care for people who underwent or will undergo HCT. To collect data, blood, and tissue samples to learn about late complications after HCT.

Eligibility: Adults age 18 and older who will undergo HCT or underwent HCT and are surviving one year or more from the date of HCT. The stem cell donors for these recipients are also needed.

Design: Recipients will have 1 visit each year. They will have a physical exam. They will answer questions about their medical history and health. They will receive screening and surveillance testing. They will complete brief questionnaires. Recipients will have blood tests. They may have tissue biopsies or specimens (such as tissue in their cheek or skin or bone marrow biopsy). Recipients will give their current address and phone number, and the same data for one or two other people, who can get in contact with them. After the first visit at the clinic, some recipients may see a doctor close to home to get the necessary information and send it to NIH. Donors will come to the clinic for 1 visit. They will answer questions about their medical history. Blood samples will be taken.