RADIATION THERAPY AS A BRIDGING AND SALVAGE STRATEGY IN PATIENTS WITH RELAPSED OR REFRACTORY MULTIPLE MYELOMA UNDERGOING BCMA‐TARGETED CAR T‐CELL THERAPY

Abstract

Introduction: Radiation therapy (RT) may be a useful bridging and/or salvage approach prior to and following B-cell maturation antigen (BCMA)-targeted chimeric antigen receptor (CAR) T-cell therapy in patients with relapsed or refractory multiple myeloma (MM). Thus, we sought to report our early experience evaluating the potential role of RT in bridging and salvage settings in MM patients undergoing CAR T-cell therapy. Methods: A multi-institutional retrospective study was conducted for consecutive MM patients who received CAR T-cell therapy between 2018 and 2022. Patients who were administered bridging RT pre-CAR T and salvage RT post-CAR T failure were identified and analyzed using descriptive and statistical analysis. Results: We retrospectively reviewed 13 patients who have been treated with RT pre- and/or post-CAR T-cell therapy infusion at two tertiary care centers [5 patients received bridging RT pre-CAR T, 4 patients received salvage RT post-CAR T failure, and 4 patients received both bridging and salvage RT]. A total of 17 sites were treated with bridging-RT with a median dose of 20 Gy (range, 4–24 Gy) and a median of 5 fractions (range, 1–12 fractions). Twelve sites were treated with salvage RT with a median dose/fractionation of 20 Gy (range, 4–30 Gy) and 5 fractions (range, 1–12 fractions). No worsening in CAR T-related toxicities occurred among the patients who were treated with bridging RT, and no significant RT-related toxicities were observed post-bridging or salvage RT. For the entire cohort, the median overall survival was 16.2 months (95% CI: 8.6 months-not reached), and the median progression-free survival was 4.1 months (95% CI: 1.07 months-not reached). The local control rate for patients receiving bridging RT and/or salvage RT was 100%, with a median follow-up after each RT course of 7.3 months. Conclusion: Our findings suggest that using RT as a bridging and salvage strategy is safe and feasible, and offers excellent local control among relapsed/refractory MM patients treated with CAR T-cell therapy infusion. Future larger studies with translational correlatives are required to assess the optimal role of RT in these settings. Keywords: Cellular therapies, Multiple Myeloma No conflicts of interests pertinent to the abstract.