fludarabine + busulfan + melphalan + thiotepa

fludarabine + busulfan + melphalan + thiotepa is an investigational multi-agent myeloablative conditioning regimen composed of the nucleoside analog fludarabine and three alkylating agents—busulfan, melphalan, and thiotepa—used prior to hematopoietic stem cell transplantation in high-risk hematologic malignancies. Fludarabine is phosphorylated intracellularly to a triphosphate that inhibits DNA polymerase, ribonucleotide reductase, and DNA synthesis, providing potent lymphodepletion and immunosuppression. Busulfan, melphalan, and thiotepa are DNA-alkylating agents that form interstrand crosslinks, resulting in irreparable DNA damage, apoptosis, and profound myeloablation; busulfan and thiotepa offer good central nervous system penetration, while melphalan has strong activity against myeloid and lymphoid cells. The combination is designed to intensify anti-leukemic and cytoreductive activity beyond standard fludarabine–busulfan or double-alkylator regimens, potentially lowering relapse at the cost of increased regimen-related toxicity, and is being explored mainly in allogeneic transplant settings for acute leukemias and other high-risk hematologic malignancies.