ABSTRACT
Hematopoietic stem cell transplantation (HSCT) is a life-saving procedure for many cancer patients. It has been widely used for treating malignant and non-malignant diseases. Since the first successful transplantation using bone marrow from a human leukocyte antigen (HLA) identical sibling in 1968, more than 800,000 patients have received HSCT worldwide with an estimated annual number of transplantations around 60,000 currently (Bach et al., 1968; Gatti et al., 1968; Eapen and Rocha, 2008). The main reasons for the wide increase in HSCT are its demonstrated efficacy in many diseases, increased donor availability due in part to using stem cells from umbilical cord blood, increased use of peripheral blood stem cells, and improved transplant outcomes. However, HSCT also has severe side effects including graft failure and graft-versus-host disease complications. These complications are major causes for transplant-related death. Patients and transplant physicians are interested in knowing survival outcomes after HSCT and are interested in comparing outcomes between treatments. The main outcome events after HSCT are overall mortality and treatment
defined as death or disease recurrence. Treatment failure is the complement of disease-free survival. Other outcomes of interest are engraftment, acute and chronic graftversus-host-disease (GVHD), treatment-related mortality (TRM) which is defined as death without cancer relapse or progression, and cancer relapse or progression. Some of these events are competing risks, where a patient may fail due to one of the k causes, and the occurrence of one of these events precludes us from observing the other events. For example, death before developing acute GVHD precludes patients from getting acute GVHD. Thus, death pre-acute GVHD is considered a competing risk for acute GVHD. Another common competing risks in HSCT studies are TRM and cancer relapse or progression.
