1011 - The Comparison of Testicular Relapse Rates in Male Children Treated with and without Testicular Boost as Part of Total Body Irradiation for Allogeneic Transplant: A Multi-Institutional Retrospective Cohort Study
Presenter(s)
K. Nishimura1, K. Goddard2,3, A. C. Lo2,3, J. Rozmus4,5, A. Li4,5, M. Rayar4,5, S. A. Milgrom6, K. Boone7, C. B. Jackson8, S. L. Wolden8, S. S. Donaldson9, S. M. Hiniker9, and J. Oh2,3; 1Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada, 2Department of Radiation Oncology, British Columbia Cancer, Vancouver, BC, Canada, 3Division of Radiation Oncology, Department of Surgery, University of British Columbia, Vancouver, BC, Canada, 4Division of Oncology, Hematology, and Bone Marrow Transplant, Department of Pediatrics, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada, 5BC Children's Hospital, Vancouver, BC, Canada, 6University of Colorado, Department of Radiation Oncology, Aurora, CO, 7Children's Hospital Colorado, Boulders, CO, 8Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 9Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA
Purpose/Objective(s):
Historical data suggested that a 4 Gy testicular boost reduced the risk of testicular recurrence. In the modern era of systemic therapy, testicular relapses are uncommon and boost practices vary across North America. The purpose of this study was to compare testicular relapse rates and survival outcomes in patients with leukemia treated with total body irradiation (TBI) with or without testicular boost.Materials/Methods:
Males aged 0–25 years with acute lymphoblastic (ALL) or acute myeloid leukemia (AML) who received TBI as part of myeloablative allogeneic transplant conditioning from 2008–2022 across four North American institutions were included. Patients with upfront testicular involvement were excluded. Three institutions delivered TBI with photon anterior posterior/posterior anterior approach, while one institution used cobalt-60 source with sweeping fields. Two institutions provided an additional electron 4Gy/1 testicular boost for most patients. Primary outcome was the testicular relapse rate. Kaplan-Meier and cox-regression multivariable analysis were performed for overall survival (OS) and relapse-free survival (RFS). Gonadal dysfunction was defined as elevated LH/FSH or low testosterone for age.Results:
A total of 221 patients were included: 132 (60%) received a testicular boost and 89 (40%) did not. Median age was 10.7 years. Diagnoses included ALL (65.5%) and AML (29.1%). Median TBI dose was 12.0 Gy (IQR 12.0–13.75 Gy). Median follow-up was 6 years. No testicular relapses occurred in the entire cohort. Five-year OS was 67% and 70% in the non-boost and boost subgroups, respectively (p=0.97). In multivariable analysis, bone marrow transplant for recurrent disease was associated with worse OS compared to primary disease (HR 1.8, CI 1.1–3.0, p=0.03), while boost status was not. Five-year RFS was 76% and 85% in the non-boost and boost subgroups, respectively (p=0.05). In multivariable analysis, boost status was no longer significant for RFS, while recurrent disease and T-ALL were associated with worse RFS. There were also institutional differences in RFS. Gonadal laboratory follow-up was available for 152 patients (56 non-boost; 96 boost). Gonadal dysfunction occurred in 35 (63%) patients in the non-boost group and 68 (71%) patients in the boost group (p=0.29).Conclusion:
Testicular relapse following TBI-based transplant was rare regardless of testicular boost. Testicular boost was not associated with improved overall or relapse-free survival in multivariable analysis. However, post-TBI gonadal dysfunction was common in both groups. These findings suggest routine testicular boost may not confer a clear survival or relapse benefit.