For adults aged 50 and older in first or second remission after induction therapy for acute myeloid leukemia, hematopoietic stem cell transplants (HSCT) from young matched unrelated donors was associated with better overall survival and lower risk for relapse than transplants from haploidentical donors, a retrospective study suggests,
Among 823 patients from the aged 50 to 75 with acute myeloid leukemia (AML) in a transplant registry, hazard ratios for both mortality and relapse were significantly higher for patients who received transplants from haploidentical siblings or offspring, compared with patients who received transplants from HLA-matched unrelated donors aged 40 or younger, reported Miguel-Angel Perales, MD, who is affiliated with Memorial Sloan Kettering Cancer Center in New York City, and colleagues.
“Our findings lend support to our hypothesis that a young [matched unrelated donor] should be the donor of choice when available. Furthermore, the data presented here suggest comparable times to transplantation in both treatment groups, confirming timely access to unrelated donors is no longer a barrier,” they wrote in Haematologica.Allogeneic transplants from matched unrelated donors have been performed for more than 30 years for treatment of patients with advanced myeloid and lymphoid malignancies. More recently, T-cell-replete bone marrow or peripheral blood transplants from haploidentical relatives, with post-transplant cyclophosphamide, tacrolimus, and mycophenolate mofetil to lower risk for graft-versus-host disease (GvHD) have become commonplace worldwide, and are established treatment options for patients with myeloid and lymphoid malignancies. There are conflicting studies suggesting that outcomes with haploidentical transplants are equivalent or superior to those seen with matched unrelated donors, the authors noted, but pointed to a 2018 study from the Acute Leukemia Working Party of the European Society for Blood and Marrow Transplant and the Center for International Blood and Marrow Transplant Research (CIBMTR). Those study results found that, among transplant recipients aged 55 through 76, graft failure, nonrelapse mortality, and overall mortality were higher when the donors were haploidentical offspring rather than HLA-matched siblings.
To see whether patients aged 50 and older with AML might benefit more with transplants from hapolidentical relatives or matched unrelated donors, the investigators used CIBMTR data to review outcomes for 823 adults with AML who received a transplant in first or second remission at one of 90 U.S. centers from 2008 through 2015.
Of this cohort, 192 patients received grafts from haploidentical donors (25% from siblings and 75% from offspring), and 631 received grafts from matched unrelated donors ranging from 18 to 40 years of age.
Although the two groups were generally similar in demographic and disease characteristics, patients in the matched unrelated donor group had significantly higher frequency of poor-risk cytogenetics (P = .03) and were significantly more likely to have received a myeloablative condition regimen than a reduced-intensity regimen (P less than .001).
In the haploidentical group, 76% of patients were in first complete remission, and the remaining 24% were in second complete remission. In the HLA-matched group the respective proportions were 83% and 17%.
The median follow-up was 42 months in the haploidentical group and 47 months in the HLA-matched group. Five-year overall survival rates were 32% and 42%, respectively.
In multivariable models controlling for donor and recipient age, sex, performance score, hematopoietic cell transplant comorbidity score, cytomegalovirus serostatus, disease status, cytogenetic risk, transplant conditioning regimen intensity and transplant period, the hazard ratio (HR) for the primary endpoint of overall mortality was 1.27 for haploidentical vs. HLA-matched grafts (P = .04). The HR for relapse risk with haploidentical transplants was 1.32 (P =.04). No significant differences in risk of nonrelapse mortality were found between the two study arms.
Bone marrow grafts from matched unrelated donors were associated with significantly higher risk for chronic GvHD than haploidentical grafts (HR, 3.12; P less than .001), but there was no difference in chronic graft-versus-host disease (GvHD) incidence between peripheral blood grafts from matched unrelated donors and haploidentical grafts.
“These data support the view that matched unrelated donor transplant with donors younger than 40 years is to be preferred,” the investigators wrote.
But in an interview, coauthor
“Even though there appears to be that clinical benefit for this older AML patient population, that benefit is not huge, and when you’re also accounting for the process of finding a donor and just getting someone into transplant, a lot of us weren’t sure if this was really going to be practice changing as the field does move into haploidentical transplants being more common,” he said.
He noted that the better outcomes among patients who received transplants from matched unrelated donors may be at least in part explained by the higher proportion of patients with unrelated donors who received myeloablative conditioning regimens. In this study, 65% of patients with haploidentical donors underwent reduced-intensity conditioning with total body irradiation, cyclophosphamide, and fludarabine.“If we do a comparison of equal conditioning regimens, are we really going to see the same outcomes in this setting? This might actually argue that, if you’re going to do a haploidentical transplant, you might start thinking about those newer, more ablative conditioning regimens,” he said.Dr. Tomlinson added that the data are reassuring, because of the modest size of the benefit, and because “many, many of our studies are showing that haploidentical transplants do almost as well as the matched ones. The big question mark will be what are the long-term outcomes? What happens after 3 years from those transplants? And that is going to take a lot more high quality, mature data.”In an editorial accompanying the study, Richard E. Champlin, MD, of the University of Texas MD Anderson Cancer Center in Houston, noted that the more frequent use of reduced-intensity conditioning used for most patients in the haploidentical group has been associated in other studies with higher relapse rates, compared with other, more intense reduced-intensity regimens.
While he agreed that the study by Dr. Perales and colleagues “should give pause for thought, however, for those considering jumping to haploidentical transplants as a preferred approach in general,” he also noted that the study’s conclusion might not apply to cases where time-to-transplant is critical, or when other conditioning and GvHD prophylaxis regimens are used.
“The ideal study would compare optimized versions of both haploidentical and unrelated donor transplants, and use “intention-to-treat” analysis, including all patients for whom a transplant is intended from the time of initial HLA typing,” he wrote.
The study was funded by grants from the National Institutes of Health and the Office of Naval Research. Dr. Tomlinson reported no relevant disclosures. Dr. Champlin did not report disclosures.
SOURCE: Perales M-A et al. Haematologica. 2020 Jan 31;105(2):407-13.
