OBJECTIVETo evaluate melphalan instead of cyclophosphamide in modified busulfancyclophosphamide regimen as a new myeloablative conditioning regimen for the treatment of myeloid malignancies patients receiving allogeneic hematopoietic stem cell transplantation （HSCT）.

METHODSThe clinic data of 94 myeloid malignancies patients undergoing allogeneic HSCT were analyzed, of which 48 patients received Bu+Cy+Flu+Ara-C, 46 cases Bu+Mel+Flu+Ara-C regimens. Rregimen-related toxicity, engraftment, graft- versus-host disease（GVHD）, infection condition, non- relapse mortality, and overall survival were compared between the two groups.

RESULTSAll patients achieved neutrophil engraftment. The incidence of grade Ⅲ-Ⅳ oral mucositis and diarrhea in BMFA group was higher than in BCFA group（P<0.05）. The incidence of acute GVHD in BMFA group was also higher than in BCFA group but without statistically significant difference（36.5% over 56.5%, P=0.100）. With a median follow up of 42 months, the incidence of no relapse mortality in BCFA group was 12.5% and 19.6% in BMFA group（P=0.400）. The relapse rate in BMFA group（4.3%）was significantly lower than in BCFA group （25.0%, P=0.009）. The overall survival rates were（71.8±6.7）% and（76.1±6.3）%（P=0.852）, and diseasefree survival rates were（67.8±8.9）% and（76.1±6.3）%（P=0.567）were comparable between BCFA group and BMFA group.

CONCLUSIONMelphalan instead of cyclophosphamide as a new myeloablative conditioning regimen had lower relapse and satisfied disease-free survival rates, but the risk of regimenrelated toxicity and GVHD should be taken into consideration.