Significance of Peri-Transplant Dynamics of Minimal Residual Disease (MRD) in Adults with Acute Myeloid Leukemia (AML) in Morphological Remission Undergoing Myeloablative Allogeneic Hematopoietic Cell Transplantation

Background: Numerous studies from others and our institution have demonstrated that the presence of minimal residual disease (MRD), detected at the time of hematopoietic cell transplantation (HCT), is strongly and independently associated with increased relapse risk and short survival in adults with acute myeloid leukemia (AML) undergoing myeloablative allogeneic HCT in morphologic complete remission (CR). In contrast, very little information is available regarding the prognostic significance of peri-transplant MRD dynamics in these patients. Since bone marrow staging studies with multiparameter flow cytometric (MFC) assessment for MRD are routinely obtained not only before but also at approximately day +28 following transplantation at our institution, we here retrospectively studied the relationship between peri-HCT MRD dynamics and post-transplant outcomes in a large patient cohort. We asked whether persistence or disappearance of MRD might identify cohorts of patients in whom post-transplant therapy was particularly indicated or unnecessary.

Patients and Methods: AML patients ³18 years of age were eligible for this retrospective analysis if they were in first or second morphologic CR or CR with incomplete blood count recovery (CRi) irrespective of the presence of MRD, underwent allogeneic HCT with myeloablative conditioning between 2006 and 2014, received peripheral blood or bone marrow as stem cell source, and had pre-HCT bone marrow staging studies available that included 10-color MFC assessments for MRD. MRD was identified as a cell population showing deviation from normal antigen expression patterns compared with normal or regenerating marrow; any level of residual disease was considered MRD^pos. We considered post-HCT MRD assessments in patients in whom bone marrow re-staging with MFC MRD analysis were obtained 28±7 days after transplantation. For this analysis, the primary endpoint of interest was overall survival, which was estimated using the Kaplan-Meier method.

Results: 311 patients were identified and included in this study. Consistent with our previous analyses, patients with MRD at the time of HCT (MRD^pos; n=76) had significantly shorter survival than MRD^neg patients (n=234; estimated 3 year post-HCT survival: 26% [95% confidence interval: 17-37%) vs. 73% [66-78%], P<0.001). 310 patients survived at least 21 days following transplantation; for 279 of these (89.7%), post-HCT MRD assessments were obtained at day +28±7 and available for analysis. 214 patients (76.7%) had no MFC evidence of MRD before and after HCT (MRD^neg/MRD^neg), 2 (0.7%) were MRD^neg/MRD^pos, 49 (17.6%) were MRD^pos/MRD^neg, and 14 (5.0%) were MRD^pos/MRD^pos. Of the 65 patients who had detectable MRD either before and/or after transplantation, 58 had decreasing levels of MRD (MRD^decr) over the peri-HCT period, whereas 7 patients had increasing MRD levels (MRD^incr) around the time of transplantation. As depicted in Figure 1, MRD^neg/MRD^neg patients had excellent long-term outcomes (survival at 3 years after day +28 MRD assessment: 76% [69-82%]), whereas both MRD^neg/MRD^pos patients died within 70 days after the day +28 MRD assessment. Interestingly, for patients who were MRDpos before transplantation, outcomes were relatively poor regardless of whether or not they had persistent MRD around day +28 after transplantation (MRD^pos/MRD^neg patients: 23% [12-36%]; for MRD^pos/MRD^pos patients: 19% [4-44%]). However, long-term survival was only observed among MRD^decr patients (at 3 years after day +28 MRD assessment: 24% [14-37%]), whereas all MRD^incr patients died a median of 97 (range: 15-808) days following the post-HCT MRD assessment (Figure 2).

Conclusion: Patients who have no evidence of MRD before and after HCT have excellent long-term outcomes. In contrast, patients who are MRD^pos before transplantation have poor survival expectations regardless of whether or not they clear MRD within the first 28 days after transplantation, but long-term survival is only found among some patients with decreasing MRD levels over the peri-transplant period. This finding suggests that patients who are MRD^pos at the time of HCT should be considered for pre-emptive therapeutic strategies given their high risk of disease recurrence regardless of the day +28 MRD information.

Figure 1

Figure 2