3580 - Combining Radiation Therapy with Bispecific Antibodies: Outcomes in Relapsed/Refractory Hematologic Malignancies
Presenter(s)
H. S. Ababneh1, A. J. Yee2, N. S. Raje3, M. J. Frigault4, P. C. Johnson2, and C. G. Patel1; 1Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 2Massachusetts General Hospital, Boston, MA, 3Division of Hematology & Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, 4Massachusetts General Hospital/ Harvard Medical School, Boston, MA
Purpose/Objective(s): We sought to describe our early experience of using radiation therapy (RT) in patients with relapsed or refractory hematologic malignancies receiving bispecific antibodies (BsAbs).
Materials/Methods: A retrospective study was conducted for consecutive patients with relapsed or refractory large-B-cell lymphoma (LBCL) or multiple myeloma (MM) who were treated with BsAbs. Patients who received RT in combination with BsAbs were identified and analyzed. RT was categorized based on its timing relative to BsAb therapy. Pre-BsAb RT included any course administered within 3 months before the first dose of BsAbs. Peri-BsAb RT encompassed courses in which at least one fraction was given between the first and last BsAb dose. Post-BsAb RT referred to any course initiated after the final BsAb dose and continuing through 3 months post-treatment. Cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) were graded according to ASTCT criteria. RT-related toxicities were assessed using CTCAE version 5.0. In-field response was evaluated using post-RT imaging and/or clinical assessment. MM patients who did not have post-RT PET/CT, but had residual abnormalities on CT imaging were classified as having partial response.
Results: A total of 26 patients, including LBCL (n=7) and MM (n=19), who received BsAbs in combination with RT were identified, with a median age at diagnosis of 63 years (range, 23–79 years). BsAbs administered for LBCL were glofitamab (n=5) and epcoritamab (n=2), while those for MM included elranatamab (n=10), teclistamab (n=5), and talquetamab (n=4). The median number of therapy lines prior to BsAb was 5 (range, 2–12), with 17 patients receiving a prior CAR T infusion. A total of 44 irradiated sites were analyzed, including pre-BsAb (n=15), peri-BsAb (n=19), and post-BsAb (n=10), with median follow-up after each RT course of 6 months (range, 0.5-17 months). Sites of RT included extremities (n=13), pelvis/groin (n=7), abdomen (n=7), spine (n=6), chest (n=6), head and neck (n=4), and paraspinal (n=1). The median dose/fractionation were 20 Gy (range, 4-41.6 Gy) and 5 fractions (range, 1-26 fractions). The in-field responses of the 42 evaluable sites were as follows: complete response (n=11, 26%) and partial response (n=31, 74%), translating into a local control rate of 100%. All sites were treated for palliative purposes with a 100% symptomatic response rate, except for three asymptomatic lymphoma patients who received pre-transplant RT. Five patients received RT to all sites of disease. Eighteen irradiated sites were bulky (=5 cm): 9 LBCL, 9 MM. None of the patients had grade 3-4 RT-related toxicities. No grade = 3 CRS or ICANS events were reported.
Conclusion: We report our early experience using RT in combination with BsAbs, highlighting its safety, feasibility, and excellent local control rates, even in bulky sites. Longer follow-up with larger cohorts is needed to assess the durability of response and the dose-response relationship.