Substitution of cyclophosphamide in the modified BuCy regimen with fludarabine is associated with increased incidence of severe pneumonia: a prospective, randomized study.

The modified busulfan-cyclophosphamide (mBuCy) regimen, combined with hydroxyurea, cytarabine and semustine, is the most frequently used myeloablative conditioning regimen for allogeneic hematopoietic stem cell transplantation in our unit. It is unknown, however, whether fludarabine can be substituted for cyclophosphamide in the mBuCy regimen. We carried out a prospective study to compare modified busulfan-fludarabine (mBuF) with mBuCy, aiming to reduce the treatment-related mortality, with non-inferiority of other outcomes. The mBuCy regimen consisted of hydroxyurea 80 mg/kg on day -10; cytarabine 2 g/m(2) on day -9; busulfan 9.6 mg/kg, intravenously on day -8 through -6; and cyclophosphamide 3.6 g/m(2) on day -5 and -4 and semustine 250 mg/m(2) on day -3. In the mBuF regimen, cyclophosphamide was substituted with fludarabine 30 mg/m(2) through day -5 to -1. Mobilized blood and marrow stem cells were collected from HLA-matched siblings. The trial was suspended due to a tendency of higher incidence of severe pneumonia in the mBuF arm, in which 105 patients were enrolled. After follow-up for another 22 months, a significantly increased incidence of severe pneumonia (31.1 %) was observed in the mBuF arm (11.6 % in mBuCy). This finding suggests that it is uncertain whether it is appropriate to substitute fludarabine for cyclophosphamide under any drug combination. This study was registered at www.chictr.org/cn under identifier ChiCTR-TRC-09000470.