SALT LAKE CITY—New research suggests outcomes may be similar whether patients receive myeloablative conditioning (MAC) or reduced-intensity conditioning (RIC) prior to haploidentical peripheral blood stem cell transplant (haploPBSCT) with post-transplant cyclophosphamide (PTCy).
Results from 2 parallel, phase 2 trials showed that MAC-PTCy-haploPBSCT and RIC-PTCy-haploPBSCT produced comparable rates of engraftment, acute and chronic graft-versus host disease (GVHD), relapse, and non-relapse mortality (NRM).
Rates of overall survival (OS) and event-free survival (EFS) were significantly higher in the MAC group. However, the fact that some RIC recipients had received prior allogeneic transplants—and none of the MAC recipients had—appeared to play a role in survival outcomes.
Junichi Sugita, MD, PhD, of Hokkaido University in Sapporo, Japan, presented these results at the 2018 BMT Tandem Meetings (abstract 50*).
To compare MAC and RIC in the context of PTCy-haploPBSCT, Dr Sugita and his colleagues conducted 2 parallel studies—JSCT Haplo 14 MAC and JSCT Haplo 14 RIC.
There were 50 patients in the MAC trial and 77 in the RIC trial. They had median ages of 36 (range, 17 to 60) and 58 (range, 22 to 65), respectively (P<0.01). There was a greater percentage of male patients among MAC recipients (82% vs 62%, P=0.028).
Diagnoses were similar between the groups and included:
- Acute myeloid leukemia—23 MAC, 34 RIC
- Acute lymphoblastic leukemia—11 MAC, 14 RIC
- Myelodysplastic syndromes/myeloproliferative neoplasms—6 MAC, 12 RIC
- Lymphoma—6 MAC, 14 RIC
- “Other”—4 MAC, 3 RIC.
Forty-eight percent (n=24) of MAC recipients and 58% (n=45) of RIC recipients were not in remission at transplant (P=0.48). There were no significant differences in disease risk index (P=0.34).
Thirty-nine percent of RIC recipients (n=30) had a history of allogeneic transplant, but none of the MAC recipients did (P<0.01).
Conditioning and prophylaxis
There were 2 MAC regimens. One consisted of fludarabine (Flu, 30 mg/m2/day on days -6 to -4) plus total body irradiation (TBI, 12 Gy on days -3 to -1). The other consisted of Flu (30 mg/m2/day on days -6 to -2), busulfan (BU, 3.2 mg/kg/day on days -6 to -3), and TBI (4 Gy on day -1).
The RIC regimen consisted of Flu (30 mg/m2/day on days -6 to -2), BU (3.2 mg/kg/day on days -4 to -3), and TBI (4 Gy on day -1).
All patients received GVHD prophylaxis consisting of cyclophosphamide (50 mg/kg/day on days 3 and 4), tacrolimus (days 5 to 180), and mycophenolate mofetil (days 5 to 60).
Siblings were the most common donors for MAC recipients (50%, n=25), followed by parents (28%, n=14), children (16%, n=8), and “other” donors (6%, n=3).
Children were the most common donors for RIC recipients (60%, n=46), followed by siblings (33%, n=25), and parents (8%, n=6).
There was no significant difference between MAC and RIC recipients when it came to human leukocyte antigen matching, cytomegalovirus serostatus, or CD34 cell dose.
However, there was a significant difference in donor-recipient gender matching (P=0.033).
Fifty-two percent (n=26) of MAC recipients and 62% (n=48) of RIC recipients had a donor-recipient gender match. Forty-two percent (n=21) and 22% (n=17), respectively, had female donor to male recipient.
Engraftment and GVHD
“Hematopoietic recovery was similar between MAC and RIC,” Dr Sugita said.
The cumulative incidence of neutrophil engraftment was 98% in MAC recipients and 94% in RIC recipients. The median time to neutrophil engraftment was 17 days and 18 days, respectively (P=0.10).
The cumulative incidence of platelet engraftment was 84% in the MAC recipients and 74% in the RIC recipients. The median time to platelet engraftment was 31 days and 37 days, respectively (P=0.32).
“Complete chimerism was achieved in all engrafted patients,” Dr Sugita noted.
There was no significant difference between MAC and RIC recipients when it came to acute or chronic GVHD.
At day 100, the cumulative incidence of grade 2-4 acute GVHD was 18% in the MAC group and 14% in the RIC group (P=0.52). Grade 3-4 acute GVHD was 8% and 5%, respectively (P=0.52).
At 2 years, the cumulative incidence of all-grade chronic GVHD was 36% in the MAC group and 27% in the RIC group (P=0.24). Moderate to severe chronic GVHD was 20% in both groups (P=1.0).
Relapse and survival
There was no significant between-group difference in NRM or relapse.
The cumulative incidence of NRM at 2 years was 20% in the RIC group and 10% in the MAC group (P=0.15). The cumulative incidence of relapse at 2 years was 45% and 36%, respectively (P=0.32).
Survival was superior in the MAC recipients. The 2-year OS was 68% in the MAC group and 44% in the RIC group (P=0.02). The 2-year EFS was 54% and 35%, respectively (P=0.04).
However, survival appeared to be affected by history of allogeneic transplant.
“Patients with a history of prior allogenic SCT have significantly worse overall survival and event-free survival,” Dr Sugita said.
Two-year OS was 31% in RIC recipients with a history of transplant and 52% in RIC recipients without a history of transplant (P=0.04). The OS was 68% in MAC recipients, all of whom had no history of transplant.
Two-year EFS was 21%, 44%, and 54%, respectively (P=0.02 for difference between 2 RIC groups).
In a multivariate analysis, conditioning regimen was not a significant predictor of NRM. The hazard ratio (HR) for RIC was 1.13 (P=0.85).
Likewise, conditioning regimen was not a significant predictor of relapse (HR=0.81, P=0.53), OS (HR=0.85, P=0.66), or EFS (HR=0.73, P=0.34).
“Our results indicate that both MAC and RIC are valid options for PTCy-haplo,” Dr Sugita said in closing.
“Ideally, a more precise comparison of MAC and RIC should be studied further in the setting of, if possible, a randomized trial.”
*Data in the abstract differs from the presentation.