Imagine a world where we could treat one of the toughest childhood cancers without exposing young patients to the full brunt of radiation—a bold shift that might just redefine standards in leukemia care. That's the exciting potential we're diving into today with groundbreaking findings from the EndRAD study, and trust me, it's sparking debates that could change lives. But here's where it gets controversial: are we ready to ditch total body irradiation entirely, even if it means rethinking decades of treatment norms? Let's unpack this step by step, breaking down the complexities for anyone new to the topic, so you can follow along easily.
The EndRAD study, officially known as a phase 2 clinical trial (NCT03509961), focused on kids and young adults battling B-cell acute lymphoblastic leukemia (B-ALL)—a type of blood cancer where immature white blood cells multiply uncontrollably in the bone marrow. Traditionally, preparing for a stem cell transplant (allogeneic hematopoietic cell transplantation, or HCT) often involves total body irradiation (TBI), a whole-body radiation treatment that wipes out the patient's immune system to make room for healthy donor cells. However, this study dared to explore an alternative: conditioning regimens without TBI, and the results were presented at the 2025 American Society of Hematology Annual Meeting and Exposition. What they discovered? Efficacy outcomes held strong, matching or even rivaling those from studies using TBI.
For beginners, let's clarify some key terms. Event-free survival (EFS) tracks the percentage of patients who live without the cancer returning or worsening, while overall survival (OS) simply measures how many survive over a period. In this trial, among patients who were next-generation sequencing (NGS) minimal residual disease (MRD)-negative—meaning sensitive tests showed no detectable cancer cells lingering before transplant—the 2-year EFS hit an impressive 76.3% (with a 95% confidence interval of 61.1% to 86.1%), and the 2-year OS was 82.0% (95% CI, 67.1% to 90.6%). These figures met the study's primary goal of demonstrating non-TBI approaches could deliver comparable results to historical TBI-based treatments. Picture this like swapping a high-risk, full-contact sport for a safer, yet equally effective training regimen—still getting the win, but with less wear and tear.
Dr. Hisham Abdel-Azim, the chief of Transplant and Cellular Therapy at Loma Linda University Health, summed it up perfectly during his presentation: 'Based upon this data, pediatric and young adult patients who are bone marrow next-generation sequencing (NGS)-minimal residual disease (MRD)-negative may consider non-TBI approaches as they choose therapy.' In simpler terms, for those kids and teens whose cancer is deeply in remission per advanced testing, skipping TBI might be a viable, less intensive option. This is the part most people miss—how personalized testing like NGS-MRD can guide these decisions, potentially sparing patients from long-term radiation side effects such as growth issues, organ damage, or even secondary cancers.
Diving deeper into the study's setup, a total of 202 patients signed up across 45 centers in North America from 2018 to 2025. The treatment arm—the experimental group with non-TBI conditioning—had 51 participants, designed to measure survival post-transplant. Most (86%) received a combo of busulfan (a chemotherapy drug), fludarabine, and thiopeta (a drug to protect stem cells). Others got variations like fludarabine with melphalan and thiopeta (6%), or an even more intensive mix including clofarabine (6%). Meanwhile, the observational arm—acting as a comparison group—had 151 patients who underwent standard myeloablative HCT, often with TBI. For context, myeloablative conditioning means using strong drugs or radiation to fully destroy the bone marrow before transplant, allowing donor cells to take over.
Dr. Abdel-Azim and his team predicted these outcomes: around 75% for 2-year EFS and 80% for OS in NGS-MRD-negative patients on non-TBI regimens. And the data aligned spot-on. But here's where it gets controversial—while TBI has been a cornerstone of transplant prep to prevent relapse, this study suggests we might not need it for certain low-risk cases. Critics might argue that TBI's broad radiation acts as a 'mop-up' for hidden cancer cells, so ditching it could risk late recurrences. On the flip side, supporters point to reduced toxicity, improving quality of life for survivors. Is this a game-changer or a gamble? The jury's still out.
Eligibility for the treatment arm was strict to ensure safety: patients aged 1 to 31 years in high-risk complete remission 1 (CR1, their first full remission) or CR2 (second remission), with no prior CAR T-cell therapy or blinatumomab (Blincyto) disqualifying them—those were allowed. Exclusions included babies under 1 year old, those with central nervous system (brain and spinal cord) relapse history, T-cell ALL or mixed-phenotype leukemia, and active disease outside the bone marrow at transplant time. These folks could join the observational arm instead. In the treatment group, the average age was 13.5 years (ranging from 2.3 to 30.5), with 51% male. Donor types varied: 37% had HLA-matched siblings (a perfect genetic match from family), 35% mismatched or haploidentical (partial family matches), 20% matched unrelated donors, and 8% unrelated cord blood. Grafts— the transplanted cells—came from bone marrow (71%), peripheral blood stem cells (21%), or cord blood (8%). At transplant, 49% were in CR1, 51% in CR2.
Wrapping up, Dr. Abdel-Azim noted: 'OS and EFS in our phase 2 non-TBI treatment arm for NGS MRD-negative B-ALL matched our hypothesis and were comparable with outcomes of patients who are MRD-negative receiving TBI in previous studies.' This echoes the broader hope that non-TBI paths could become the new standard for select patients, reducing complications without sacrificing cure rates. As with many medical breakthroughs, it's a delicate balance—advances like this build on prior research, showing how tailored treatments can evolve.
For transparency, Dr. Abdel-Azim disclosed consultancies with Kite, Novartis, Adaptive (including research funding), Vertex, and Johnson & Johnson—standard in clinical research to highlight potential biases.
The full details are in the reference: Abdel-Azim H, Quigg T, Kapoor N, et al. High event-free (EFS) and overall survival (OS) after non-total body irradiation (TBI) conditioning and allogeneic hematopoietic cell transplantation (HCT) in next-generation-sequencing minimal residual disease (NGS-MRD) negative B-acute lymphoblastic leukemia (B-ALL): Results from the EndRAD trial (PTCTC ONC1701). Blood. 2025;146(suppl 1):163. doi:10.1182/blood-2025-163.
Stay up to date on recent advances in the multidisciplinary approach to cancer. Sign up for our newsletter to keep learning about these life-saving innovations.
What do you think? Should we embrace non-TBI conditioning for B-ALL transplants, or is the risk of relapse too high without that extra radiation layer? Do you agree this could revolutionize pediatric oncology, or are there hidden downsides we haven't considered? Share your thoughts in the comments—let's discuss!
