Among the 24 patients in the CLOVER WaM subset who received iopofosine I 131 immediately after BTK inhibitor failure, nearly four in five achieved a major response (79.2%), and the overall response rate reached 87.5%, with responses lasting more than 16 months. Those numbers matter because BTKi-refractory Waldenström macroglobulinemia is exactly where treatment options thin out, and this subset represents the patients most likely to wind up in a physician’s office with few clear paths forward.
Cellectar Biosciences will present the full subset analysis at the International Workshop for Waldenström Macroglobulinemia, drawing on data from the Phase 2b CLOVER WaM trial, which completed enrollment in 2024 with 55 patients in the per-protocol population. The broader per-protocol cohort showed an 83.6% overall response rate and a 61.8% major response rate, so the BTKi-immediate subset outperforms the full trial on both measures. That gap suggests sequencing matters: patients who moved to iopofosine I 131 right after a BTKi, rather than cycling through additional lines first, appear to respond more deeply and durably.
The mechanism behind that pattern is worth watching. Iopofosine I 131 uses a phospholipid drug conjugate to deliver iodine-131 selectively to malignant cells, and the hypothesis is that earlier use preserves tumor biology that makes the drug’s targeting more effective. The dataset is small, so that explanation is inference rather than established fact, but it is the kind of question a Phase 3 design would need to answer. Iopofosine I 131 received FDA Breakthrough Therapy Designation for relapsed or refractory WM in June 2025, which gives Cellectar an expedited path to work with the agency on exactly that design question.
The concrete marker to track from the IWWM presentation is whether Cellectar discloses a depth-of-response breakdown, specifically very good partial response or better rates within the BTKi-immediate subset. If that fraction holds up against the headline MRR, it strengthens the case for a registration trial that enrolls patients at second line rather than later, which is where the drug’s commercial and clinical argument is strongest.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
