On June 1, 2026 Cellectar Biosciences, Inc. (NASDAQ: CLRB), a late-stage clinical biopharmaceutical company focused on the discovery and development of drugs for the treatment of cancer, reported that efficacy results from a subset of patients treated with iopofosine I 131 immediately post-Bruton Tyrosine Kinase inhibitor (BTKi) therapy in the Company’s Phase 2 CLOVER WaM clinical trial of iopofosine I 131 to treat relapsed or refractory (r/r) Waldenström macroglobulinemia (WM) will be highlighted today in a poster presentation at the American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting (ASCO) (Free ASCO Whitepaper) taking place May 29-June 2, 2026 in Chicago, Illinois.

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"We are highly encouraged by these results from the CLOVER WaM study, which demonstrate compelling efficacy and durable responses with iopofosine I 131 in the particularly challenging patient population that has progressed following BTKi therapy. I look forward to highlighting these positive outcomes at this year’s ASCO (Free ASCO Whitepaper)," said Jarrod Longcor, chief operating officer of Cellectar Biosciences. "Patients with immediate post-BTKi disease represent a distinct clinical population within WM that is characterized by limited responses and rapid disease progression after BTKi discontinuation. In addition, there is no FDA-approved treatment that reliably provides durable disease control in this setting. These outcomes give us even greater confidence in the potential of iopofosine to be effective in an earlier line setting as will be evaluated in the planned Phase 3 confirmatory study."

In the CLOVER WaM Phase 2 clinical trial, eligible WM patients received greater than two prior therapies and had symptomatic disease requiring therapy. Treatment consisted of two cycles of iopofosine I 131 administered at 15 mCi/m2 on days 1 and 15 of each 57-day cycle. The primary efficacy endpoint was major response rate (MRR). This subset analysis assessed a modified intent-to-treat (mITT) population (all patients who received ≥60 mCi total administered dose of iopofosine I 131), and whose immediately prior treatment was a BTKi. Data cut off for this analysis was January 16, 2026.

Highlights of the Data:

Iopofosine I 131 demonstrated significant efficacy (n=24):
100% clinical benefit rate
87.5% overall response rate
79.2% major response rate, partial response or better
Median duration of response (DOR) of 16 months (range: 7.3 – 25.4 months)
20% of patients exceeded 30 months DOR
The treatment was well-tolerated with a manageable toxicity profile with cytopenias as the only Grade 3 or greater adverse event.
"These new data further reinforce the compelling clinical profile of iopofosine I 131, demonstrating meaningful efficacy in a subset of WM patients following BTKi treatment," said James Caruso, president and chief executive officer. "The strength and consistency of response observed in this post-BTKi population underscore iopofosine’s potential to address a critical unmet need in the second line setting and beyond. Based on these findings, we plan to pursue accelerated approval in the U.S. and initiate a confirmatory Phase 3 study in the fourth quarter of 2026. We remain committed to bringing iopofosine to the thousands of patients who may benefit from this therapy."

Details of the poster presentation are as follows:

Title: "Iopofosine I-131 after BTK inhibitors in Waldenström macroglobulinemia: CLOVER-WaM subgroup efficacy and safety"
Poster: 592
Date/Time: June 1, 2026, 9:00am – 12:00pm CDT
Presenter: Jarrod Longcor

(Press release, Cellectar Biosciences, JUN 1, 2026, https://www.cellectar.com/investors/news-events/press-releases/detail/393/cellectar-biosciences-to-highlight-compelling-new-efficacy-data-from-phase-2b-clover-wam-study-of-iopofosine-i-131-in-rr-waldenstrm-macroglobulinemia-at-the-american-society-of-clinical-oncology-annual-meeting [SID1234666301])