Alternative Donor Hematopoietic Transplantation For Patients Older Than 50 Years With AML In First Complete Remission: Unrelated Donor and Umbilical Cord Blood Transplantation Outcomes

Post-remission allogeneic transplantation is increasingly used for treatment of the high-risk acute myeloid leukemia (AML) affecting older adults. We analyzed 740 adults over age 50 with AML in first complete remission (CR1) to compare the effectiveness of volunteer unrelated donor (URD) and umbilical cord blood (UCB) graft sources in providing a successful transplant. For prospective cases reported (2005-2010) to the Center for International Blood and Marrow Transplant Research and Eurocord, we evaluated 8/8 HLA allele matched (at HLA-A, -B, -C, -DRB1) n=441; 7/8 matched URD n=94 and UCB n=205 for the outcomes of engraftment, treatment related (non-relapse) mortality (TRM), relapse, leukemia free survival (LFS) and overall survival (OS) using the cumulative incidence and Kaplan-Meier estimators and multivariate Cox regression modeling. Patient age (median 58, range 50-75), gender and CMV serostatus were similar across the treatment groups. However, UCB recipients were less likely to achieve CR within 8 weeks, more likely to report Intermediate and unfavorable risk cytogenetics, more likely to receive reduced-intensity conditioning compared to myeloablative conditioning regimens, and receive cyclosporin rather than tacrolimus-based GVHD prophylaxis.

After a median follow-up of 50, 61 and 37 months in 8/8 URD, 7/8 URD and UCB grafts, neutrophil and platelet recovery was slower in UCB compared to URD recipients; the day-42 incidence of neutrophil recovery in UCB recipients was 85% compared to 98% and 92% in 8/8 and 7/8 URD recipients. While there were no significant differences in rates of grade II to IV acute GVHD (35%, 36% and 44% in UCB, 8/8 URD and 7/8 URD recipients respectively), the 3-year incidence of chronic GVHD was significantly lower in UCB recipients (28% compared to 53% and 59% in 8/8 and 7/8 URD recipients. Compared to 8/8 URD transplants, multivariate analysis confirmed higher TRM after transplantation of UCB grafts, but only in the first 3 months (HR 2.83, p<0.0001) with similar risks thereafter (HR 1.00, p=0.99). Compared to 8/8 URD transplants, TRM was higher after 7/8 URD transplants (HR 1.73, p=0.005). There were no significant differences in relapse risks between the three groups; compared to 8/8 URD transplants, relapse risks after UCB and 7/8 URD transplants were HR 1.15, p=0.36 and HR 0.86, p=0.47, respectively. These hazards yielded higher adjusted 3-year LFS after 8/8 URD (39% [95% CI 34%-43%]) compared to 7/8 URD (34% [95% CI 24%-43%]) and UCB transplants (28% [95% CI 22%-35%]), p=0.015) and adjusted 3-year OS of 43% (95% CI 38%-48%), 37% (95% CI 27%-46%) and 30% (95% CI 23%-37%), respectively (p=0.003). Relapse risks were greater in patients with intermediate or unfavorable risk cytogenetics, independent of graft type and leukemia-free and overall survival were also worse in patients with unfavorable risk cytogenetics and in patients over age 60. For the older population with AML, allotransplantation in CR1 can provide extended leukemia-free survival for 30%-43% of patients using any of these graft sources. While 8/8 URD transplants are preferred for patients who can promptly obtain a well-matched URD, for ethnic or racial minorities, UCB grafts provide a meaningful chance of extended LFS, even though nearly all UCB grafts are HLA mismatched.

Additionally, the rapid availability of UCB provides effective therapy for older patients with expected short initial remissions: settings where ongoing consolidation therapy has not been effective in limiting risks of relapse. Later TRM and relapse rates were similar, lower risks of chronic GVHD and the need for long-term immunosuppression and its morbidities may be of particular value for these older patients. These encouraging results suggest that allotransplantation need not be withheld from older patients and for clinically suitable AML patients, can produce extended and even curative long-term survival.