Extramedullary relapses after allo-HCT in AML patients

There is a paucity of data on the mechanism and clinical impact of Extramedullary Relapse (EMR) in Acute Myeloid Leukemia (AML) patients undergoing Allogeneic Hematopoietic Cell Transplantation (allo-HCT). Noura Alhashim and colleagues from King Faisal Specialist Hospital and Research Center, Saudi Arabia, retrospectively studied the frequency of EMR and Bone Marrow Relapse (BMR) and evaluated the differences between relapse in the Bone Marrow (BM) and extramedullary sites in terms of risk factors and clinical course. The results of the study were reported in Bone Marrow Transplantation in January 2018.

Overall, 215 AML patients in Complete Remission (CR) who underwent allo-HCT using myeloablative conditioning from a matched sibling donor at the King Faisal Specialist Hospital and Research Center between 2005 –2015 were retrospectively analyzed in this study. Relapse occurred in 77 patients post-allo-HCT with patients experiencing either BMR (n = 45) or EMR (n = 32).

Key findings:

• Post-relapse median Overall Survival (OS) for all relapses: 10 months (95% CI, 4.839 – 15.161)
• Post-relapse median OS for patients in the EMR and BMR group: 14 vs 8 months, P = 0.4
• Post-relapse death associated significantly with gender, treatment modality, and time from allo-HCT to relapse: ≥12 vs <12 months
• Patients with extramedullary disease were at higher risk of post-relapse mortality: HR = 2.4, P = 0.04
• Compared to females, males were more likely to develop EMR: Odds Ratio (OR) = 3.2, P = 0.01
• There was a trend to develop EMR if transplanted in second Complete Remission (CR2): OR = 0.38, P = 0.06

The authors concluded that the findings of their study demonstrates that in a homogenous population, EMR represent a large proportion of AML relapses post allo-HCT (42%). Additionally, the time to relapse and post-relapse survival were similar between EMR and BMR. Intriguing, this is the first study to report male gender as a risk factor for EMR.

The authors further noted that due to the retrospective nature of the study and the young population of the patient group which probably does not represent the AML patient population, the findings of their study should not be generalized to all AML patients.