Myeloablative Conditioning with Intravenous Busulfan In One Daily Dose and Fludarabine (BUF) for HLA-Identical Sibling Allogeneic HSCT In Myeloid Malignancies

There is a need to improve the conditioning regimens for allogeneic HSCT, both reducing the regimen related toxicity and improving the anti-leukemic effect. The myeloablative (MA) regimen consisting in intravenous (iv) busulfan (BU) with fludarabine (F) might be a better option than the conventional BU-CY (Cyclophosphamide) combination, since BU and F act synergistically against leukemia cell lines and previous studies with iv BU-F conditioning have reported an improved safety profile over BU-CY.

We aimed to evaluate the efficacy and safety of the MA BU-F regimen, delivering iv BU in a one-daily dose after F infusion, since previous pharmacologic and clinical data supported its safety compared with the standard four-daily doses in the HLA identical sibling allogeneic HSCT setting.

One hundred thirty seven consecutive adult patients with myeloid malignancies from nine Spanish institutions were recruited from 2005 to 2011. They had a median age of 47 years (range 19–74) and 60% were males. Diagnosis were AML: 80 (58.4%), AML secondary to MDS: 24 (17.5%), MDS: 23 (16.8%) and MPD: 10 (7.3%). At HSCT, the disease stage was 1^st CR or untreated in 85 (62%) and more advanced stage in 52 (38%) cases. Patients having Karnofsky < 90% and Sorror CI >1 accounted for 11.7% and 38.3%.

The conditioning regimen consisted in F, 40 mg/m2 daily for 4 days (total dose 160 mg/m2) followed by BU, one-daily IV 3.2 mg/kg infusion (total dose 12.8 mg/kg). GVHD prophylaxis consisted in cyclosporine and methotrexate. HSC infusion and post-transplant supportive measures and follow-up were made according each institution policies.

Donor graft source was peripheral blood (PB) in 93 (67.9%) and bone marrow (BM) in 44 (32.1%) cases. Median CD34+ cells infused were 4.5 millions/kg (range 0.6–17.8). All but one patient engrafted, with a median of 15 days (range 8–49) to >0.5 ×10E9 PMN/L and 13 days (range 7–149) to >20 ×10E9 platelets/L. The most frequent toxicity was mucositis, which was grade >1, in 68.8% cases. Three patients had hepatic SOS grade >1, and all of them resolved. Median hospitalization time was 30 days (range 17–114). Acute GVHD grade 2–4 incidence was 25% with a median of 32 days (range 12–87) to GVHD onset. The day-100 mortality was 4.8%. The chronic GVHD incidence in 114 patients at risk is 61.4%, with 37.7% of cases in extended form. At the time of this analysis, the median follow-up is 12 months (range 1–74). Crude survival data showed 106 (77.4%) patients remaining alive and 106 (77.4%) relapse free. Overall, 31 patients have died, 19 relapse-related (13.9%) and 12 (8.8%) due to transplant related mortality. Actuarial survival at 12 months is 79.4% and disease free survival is 71.3% in the whole series. Kaplan-Meier analysis showed that advanced age, comorbidities or advanced disease status at HSCT did not predict an inferior outcome.

In conclusion, in the HLA identical sibling allogeneic HSCT setting, the BU-F regimen provides an adequate control of myeloid malignancies, with low regimen related toxicity and both reduced day-100 and non-relapse related mortality.

Lahuerta:Janssen: Honoraria; Celgene: Honoraria.