Comparable Results Between 8 and 12 Gray TBI in Combination With Fludarabine and Post‐Transplant Cyclophosphamide in MRD‐Negative but Not in MRD‐Positive Acute Lymphoblastic Leukemia Patients Transplanted in First Complete Remission.

Background: The optimal TBI dose for ALL patients undergoing allogeneic SCT is still not clearly defined. Methods: Single‐center retrospective analysis of high‐risk ALL patients in CR1 treated with 8 Gy (n = 22) or 12 Gy (n = 50) TBI in combination with fludarabine and PTCy. Median patient age in the 8 Gy TBI cohort was 63 (37–79) and 37 (18–56) in the 12 Gy TBI cohort and median follow‐up time was 21 months (range 1–92). Results: OS and LFS at 2 years after 8 Gy were 65% and 55% versus 74% and 74% after 12 Gy (p = 0.3 and p = 0.2, respectively). CIR and NRM at 2 years were 27% and 14% after 8 Gy versus 4% and 20% after 12 Gy (p = 0.004 and p = 0.4, respectively). MRD‐positive (+) patients (n = 26) receiving 12 Gy (n = 19) showed better OS (p = 0.01), LFS (p = 0.009), GRFS, lower CIR (p = 0.02), and similar NRM than did MRD+ patients receiving 8 Gy (n = 7). MRD‐negative (−) patients (n = 38) receiving 12 Gy (n = 27) had similar OS, LFS, GRFS, lower CIR, and higher NRM (p = 0.04) than did MRD− patients receiving 8 Gy (n = 11). Conclusion: Our study demonstrates that 8 Gy TBI in comparison to 12 Gy TBI results in low NRM but a high relapse rate with similar OS, LFS, and GRFS. In MRD+ high‐risk ALL patients, allogeneic SCT with 12 Gy TBI leads to improved OS, LFS, GRFS, and a low relapse rate. Prospective studies comparing the different treatment regimens with larger MRD patient cohorts are needed to confirm this data. [ABSTRACT FROM AUTHOR]