FLORHAM PARK, N.J., October 15, 2026
Cellectar Biosciences, Inc. (NASDAQ: CLRB) presented positive subgroup efficacy findings from its Phase 2b CLOVER WaM clinical trial evaluating iopofosine I 131 in patients with relapsed or refractory Waldenström macroglobulinemia (WM) previously treated with a Bruton tyrosine kinase inhibitor (BTKi). The findings were presented at the International Workshop for Waldenström Macroglobulinemia, held October 14–16, 2026, in Palm Springs, California. In a subgroup of 24 patients treated immediately after BTKi therapy, iopofosine I 131 achieved an overall response rate (ORR) of 87.5%, a major response rate (MRR) of 79.2% and a clinical benefit rate (CBR) of 100%. Median duration of response was 16 months, while treatment-free survival reached 19.1 months. The analysis included a heavily pretreated population, with 75% of patients classified as BTKi-refractory and more than 54% having received multiple BTKi therapies. Cellectar is advancing plans for a randomized Phase 3 confirmatory trial in patients who have received prior first-line treatment and BTKi therapy. The company expects to dose the first participants in the first quarter of 2027 and anticipates submitting an application for U.S. accelerated approval in the first half of 2027, subject to regulatory requirements and the development program’s progress.
Subgroup Analysis Shows Responses Following BTK Inhibitors
The CLOVER WaM subgroup analysis included 24 patients who received iopofosine I 131 immediately after a BTKi-containing regimen. Patients had received a median of three prior lines of therapy, with a range of two to seven. Approximately 17% had TP53 mutations, while 29% were MYD88 wild type—characteristics identified in the release as associated with greater treatment resistance or more rapid disease progression. Within this subgroup, the overall response rate was 87.5%, and the major response rate was 79.2%. The clinical benefit rate reached 100%, with a median duration of response of 16 months and treatment-free survival of 19.1 months. Cellectar also reported that treatment-emergent adverse events occurred in fewer than 10% of patients, with cytopenias the only reported Grade 3 or higher treatment-emergent adverse event in this analysis. The findings were derived from the trial’s 12-month follow-up dataset. Although the results indicate clinical activity in this subgroup, the analysis involved a relatively small number of patients and does not by itself establish comparative efficacy. Further evaluation in a randomized confirmatory study will be important to characterize the treatment’s benefits and risks in this patient population.
Targeted Radioisotope Therapy for Relapsed or Refractory WM
Iopofosine I 131 is a targeted radiopharmaceutical developed using Cellectar’s proprietary Phospholipid Drug Conjugate (PDC) platform. The investigational product uses a phospholipid drug-conjugate approach to deliver iodine-131, a therapeutic radioisotope, to cancer cells. Its development for WM is intended to address patients whose disease has relapsed or become resistant to available therapies, including BTK inhibitors. Cellectar Chief Operating Officer Jarrod Longcor said the new analysis adds to the evidence supporting further investigation of iopofosine I 131 after BTKi therapy. He highlighted the response rates, duration of response and treatment-free survival reported in the subgroup, alongside the company’s view that a treatment acting independently of the BTK pathway may offer a different therapeutic approach. These are company interpretations of the data; the findings remain clinical-trial results and do not establish that the therapy will be effective for all patients who develop BTKi resistance. Cellectar said the candidate has received Breakthrough Therapy Designation from the U.S. Food and Drug Administration (FDA), along with additional orphan-drug, rare-pediatric-disease and Fast Track designations for various cancer indications. The European Medicines Agency has also granted PRIME designation. These designations support regulatory development but do not constitute marketing approval.
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Phase 3 Trial and Potential Accelerated Approval Pathway
Cellectar is initiating site selection and other preparations for a randomized Phase 3 confirmatory clinical trial in patients with WM following first-line treatment and BTKi therapy. The planned study is expected to evaluate progression-free survival (PFS) as its primary endpoint, with first-patient dosing anticipated in the first quarter of 2027. The company also plans to pursue a U.S. New Drug Application for accelerated approval in the first half of 2027. According to Cellectar, its CLOVER WaM dataset includes elements intended to align with FDA expectations for an accelerated approval pathway, including major response rate supported by duration of response as surrogate measures reasonably likely to predict clinical benefit, durable responses in a high-unmet-need population and at least 12 months of follow-up across all patients. Any regulatory submission and decision will depend on the applicable requirements and FDA review. Cellectar is a late-stage clinical biopharmaceutical company developing treatments for cancer. In addition to iopofosine I 131, its pipeline includes CLR 121125, an iodine-125 Auger-emitting program being evaluated in a Phase 1b study for triple-negative breast cancer, and CLR 121225, an actinium-225-based program targeting solid tumors, including pancreatic cancer. The company is also advancing other preclinical PDC-based therapeutic programs. The next milestones for iopofosine I 131 are the planned confirmatory study and the company’s anticipated regulatory submission.
Source::Cellectar Biosciences press release
