Outcomes and Prognostic Factors of Second Allogeneic Hematopoietic Cell Transplantation in Patients with Acute Lymphoblastic Leukemia: A Study from the Adult Acute Lymphoblastic Leukemia Working Group of the Japanese Society for Transplantation and Cellular Therapy
Authors: Kamijo Kimimori , Shimomura Yoshimitsu , Tachibana Takayoshi , Najima Yuho , Aoki Jun , Akahoshi Yu , Tanaka Masatsugu , Doki Noriko , Uchida Naoyuki , Ohigashi Hiroyuki , Kobayashi Hikaru , Ota Shuichi , Nara Miho , Fujiwara Shinichiro , Mori Yasuo , Kanda Yoshinobu , Ichinohe Tatsuo , Atsuta Yoshiko , Arai Yasuyuki 
Published: December 2023

Background
Allogeneic hematopoietic cell transplantation (allo-HCT) is a curative treatment option frequently used in patients with acute lymphoblastic leukemia (ALL). However, relapse after allo-HCT remains the main concern because it is associated with poor outcomes, with a long-term survival rate &lt; 10 %. There is no standard treatment for patients with ALL who relapsed after allo-HCT.
Second allo-HCT (allo-HCT2) is a curative treatment option for patients with ALL who relapsed after the first allo-HCT (allo-HCT1). However, data on allo-HCT2 in patients with ALL are limited, and the indications and outcomes of allo-HCT2 are unclear.
Therefore, this study aimed to investigate the outcomes and prognostic factors of patients who underwent allo-HCT2 after ALL relapse.
Methods
This study included 425 adult patients with ALL who underwent allo-HCT2 after relapse between January 2001 and December 2020. The primary endpoint was 2-year overall survival (OS), which was evaluated using the log-rank test. Prognostic factors for the primary endpoint were evaluated using the multivariable Cox proportional hazards model. The variables considered in the Cox proportional hazards model are listed in the Table. The impacts of the candidate factors are shown as hazard ratios (HRs) and 95% confidence intervals (CIs). Additionally, we performed an analysis stratified by disease and disease status because Philadelphia chromosome (Ph)-positive B-ALL could affect the treatment and disease status at allo-HCT2 and the outcome.
Results
The median age at allo-HCT2 was 36 years (interquartile range; 27-48 years) and 220 patients (52%) were male. According to the Eastern Cooperative Oncology Group, 94 patients (22%) had a performance status of &gt; 2. There were 235 patients (55%) with Ph-negative B-ALL, 122 patients (29%) with Ph-positive B-ALL, and 68 patients (16%) with T-ALL. Regarding disease status at allo-HCT2, 217 patients (51%) had any complete response (CR). One hundred forty-eight patients (35%) received myeloablative conditioning regimen. Ninety patients (21%) received related bone marrow (BM) or peripheral blood (PB) transplantation, 137 patients (32%) received unrelated BM or PB transplantation, and 198 patients (47%) received unrelated cord blood (CB) transplantation.
The median observation time of survivor after allo-HCT2 was 22.3 (interquartile range; 6.3-82.5) months and 2-year OS was 28.0% (95% CI, 23.7-32.4). After stratified disease and disease status, the 2-year OS was 56.5% (95% CI, 44.6-66.8), 31.7% (95% CI, 24.0-39.7), 21.5% (95% CI, 10.6-34.9), and 13.1% (95% CI, 8.4-18.8) in any CR (Ph-positive B-ALL), any CR (other), active disease (Ph-positive B-ALL), and active disease (other), respectively ( P &lt; 0.001) (Figure).
In multivariable analysis, Ph-positive B-ALL (HR, 0.48; 95% CI, 0.36-0.65; P &lt; 0.001), tacrolimus-based GVHD prophylaxis at allo-HCT2 (HR, 0.72; 95% CI, 0.54-0.95; P = 0.022) were identified as significantly positive prognostic factors for 2-year OS, while allo-HCT1 to allo-HCT2 &lt; 12 months (HR, 1.38; 95% CI, 1.02-1.88; P = 0.038), relapse within 12 months after allo-HCT1 (HR, 1.37; 95% CI, 1.01-1.85; P = 0.043), ECOG PS &gt; 2 (HR, 1.89; 95% CI, 1.44-2.49; P &lt; 0.001), active disease at allo-HCT2 (HR, 1.88; 95% CI, 1.46-2.42; P &lt; 0.001), unrelated BM or PB transplantation at allo-HCT2 (HR, 1.78; 95% CI, 1.22-2.59; P = 0.003), and CB transplantation at allo-HCT2 (HR, 1.54; 95% CI, 1.09-2.18; P = 0.013) were identified as significantly negative prognostic factors for 2-year OS.
Conclusion
In this study, we demonstrate that the 2-year OS was 28.0% in patients with ALL who underwent allo-HCT2 and identified the prognostic factors that may guide patients to benefit from allo-HCT2.