A Single-Arm, Prospective Study of TBI+BUMEL as Conditioning for SCT2 in Patients With Malignant Hematologic Diseases

Each year, over 20,000 patients in China undergo hematopoietic stem cell transplantation (HSCT). Unfortunately, the prognosis in patients with disease relapse or graft failure is often inferior. A second allogeneic hematopoietic stem cell transplantation (SCT2) has emerged as a vital salvage therapy option. Despite varying prognoses, most patients undergoing SCT2 have a five-year overall survival (OS) rate of less than 30%. The primary challenges of SCT2 include treatment strategy, immune regulation, complication management, and transplantation technique improvements. By optimizing these key aspects, SCT2 can effectively address issues that arose after the first transplant, reduce complications, and provide more effective treatment for patients. Clinical practice indicates that SCT2 is crucial in treating various hematologic diseases. For patients who failed the first transplant (SCT1), SCT2 can more effectively treat the primary disease, provide timely hematopoietic engraftment, extend survival time, and improve the quality of life. Additionally, the successful application of SCT2 provides clinicians with more treatment options and hope. Currently, the modified BU/CY conditioning regimen, which consists of busulfan (BU) and cyclophosphamide (CY), is commonly used in SCT1 in China. However, for patients who relapse after SCT1, these drugs may become ineffective, and the physical condition often worsens, with a higher likelihood of infections and organ dysfunction. Therefore, finding new conditioning regimens is crucial. Studies have shown that a melphalan (MEL)-based conditioning regimen may have better outcomes for patients with acute myeloid leukemia (AML) compared to a Cy-based regimen. The Conditioning regimen that includes total body irradiation (TBI) has also been considered effective for patients with acute leukemia. Thus, low-dose TBI combined with a BU + MEL regimen could be a promising conditioning regimen for SCT2. In the investigators' preliminary stud