Hematopoietic Cell Transplantation for Children with Acute Megakaryoblastic Leukemia without Down Syndrome

Acute megakaryoblastic leukemia (AMKL) accounts for 10% of childhood acute myeloid leukemia. Although AMKL patients with Down syndrome (DS-AMKL) have an excellent survival rate, patients with non-DS-AMKL experience poor outcomes. Despite therapeutic advances, including use of intensified treatment protocols, there is no consensus on the optimal treatment strategy for non-DS-AMKL. Some study groups recommend hematopoietic cell transplantation (HCT) for patients with non-DS-AMKL in the first complete remission (CR1); however, it is unclear whether HCT in CR1 improves outcomes of these patients.

To assess outcomes and risk factors of HCT for patients with non-DS-AMKL, we retrospectively analyzed 203 patients with non-DS-AMKL (male, 95; female, 108) who underwent first HCT between 1986 and 2015 using data from the Japan Society for Hematopoietic Cell Transplantation. The median age at the time of HCT was 2 years (range, 0-16). Out of 203 patients, 12 had translocation t(1;22)(p13;q13), 18 had monosomy 7, 21 had complex karyotype, and 109 had other chromosomal abnormalities. Bone marrow transplantation (BMT) was performed for 114, cord blood transplantation (CBT) for 74, and peripheral blood stem cell transplantation (PBSCT) for 15 patients. Seventy-eight patients underwent HCT from related (HLA-matched, 43; HLA-mismatched, 35), 108 from unrelated (HLA-matched, 56; HLA-mismatched, 52), and 17 from autologous donors. Ninety-two patients underwent HCT in CR1, 21 in the second CR (CR2), and 90 in non-CR. Myeloablative conditioning (MAC) regimen was defined as the use of total body irradiation (TBI) ≥8 Gy, administration of busulfan >8 mg/kg or melphalan >140 mg/m². All other regimens were included in reduced intensity conditioning (RIC) regimen. MAC regimen was used for 192 and RIC regimen for 11 patients.

Median duration of follow-up after HCT was 713 days (range, 3-10008). Out of 203 patients, 183 (90%) exhibited engraftment. Sixteen out of 20 patients who did not exhibit engraftment underwent HCT in non-CR. In the entire cohort, 5-year overall survival (OS) and event free survival (EFS) rates were 43% and 38%, respectively. Seventy-two patients died of disease relapse and 42 died of transplantation-related complications. Five-year OS/EFS rates were not significantly different between BMT (48%/43%), CBT (35%/31%), and PBSCT (31%/27%) (p = 0.221/p = 0.087). In allogeneic HCT, 5-year OS/EFS rates were significantly lower in patients who underwent HCT from HLA-mismatched donors (27%/22%) than those from HLA-matched donors (52%/47%) (p < 0.001/p < 0.001). Five-year cumulative incidence (CI) of relapse after HLA-mismatched HCT (64%) was significantly higher than that after HLA-matched HCT (45%) (p = 0.006). Five-year OS/EFS rates were not significantly different between patients with translocation t(1;22)(p13;q13) (50%/42%), those with monosomy 7 (65%/59%), and those with complex karyotype (61%/52%) (p = 0.094/p = 0.111). Five-year OS/EFS rates of patients who underwent HCT in CR1 (72%/64%) were significantly higher than those of patients who underwent in CR2 (23%/13%) and non-CR (16%/16%) (p < 0.001/p < 0.001). Five-year CI of relapse was significantly lower in CR1 (28%) than in CR2 (73%) and non-CR (73%) (p < 0.001). Five-year non-relapse mortality was significantly higher in non-CR (27%) than in CR1 (15%) and CR2 (14%) (p = 0.022). Among the 92 patients who underwent HCT in CR1, 3-year CI of relapse in patients who received RIC (67%) was significantly higher than that in patients who received MAC regimen (25%) (p = 0.021). Five-year OS/EFS rates associated with HCT from HLA-mismatched (70%/63%) and HLA-matched donors (77%/59%) were not significantly different (p = 0.609/p = 0.761). In the multivariate analysis for 5-year OS, HCT in CR2 and non-CR was found to be a significant risk factor (hazard ratio, 5.16; 95% CI, 3.36-7.92; p < 0.001).

In conclusion, multivariate analysis confirmed that HCT in CR1 was a good prognostic factor for 5-year OS. Risk stratification in patients with non-DS-AMKL should be established to determine the indication for HCT in CR1.