Cellectar Biosciences to Highlight Compelling New Efficacy Data from Phase 2b CLOVER WaM Study of Iopofosine I 131 in r/r Waldenstrom Macroglobulinemia at the American Society of Clinical Oncology Annual Meeting

Approximately 80% Major Response Rate and Duration of Response Exceeding 16 Months in 
Subset Analysis of Patients Treated with Iopofosine I 131 Immediately Post-BTKi Therapy

Plans to Initiate Phase 3 Confirmatory Clinical Trial in 4Q26

FLORHAM PARK, N.J., June 01, 2026 (GLOBE NEWSWIRE) -- Cellectar Biosciences, Inc. (NASDAQ: CLRB), a late-stage clinical biopharmaceutical company focused on the discovery and development of drugs for the treatment of cancer, today announced 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 Annual Meeting (ASCO) taking place May 29-June 2, 2026 in Chicago, Illinois.

“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,” 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

Following the presentation, the full analysis will be available on the Company’s website here.

About Cellectar Biosciences, Inc.
Cellectar Biosciences is a late-stage clinical biopharmaceutical company focused on the discovery and development of proprietary drugs for the treatment of cancer, independently and through research and development collaborations. The company’s core objective is to leverage its proprietary Phospholipid Drug Conjugate™ (PDC) delivery platform to develop the next-generation of cancer cell-targeting treatments, delivering improved efficacy and better safety as a result of fewer off-target effects.

The company’s product pipeline includes iopofosine I 131, which is a PDC designed to provide targeted delivery of iodine-131 (radioisotope). Iopofosine I 131 has been tested in Phase 2b trials as a treatment for relapsed or refractory Waldenström Macroglobulinemia (WM), in relapsed or refractory multiple myeloma (MM) and central nervous system (CNS) lymphoma. The CLOVER-2 Phase 1b study is evaluating iopofosine I 131 in pediatric patients with high-grade gliomas, for which Cellectar is eligible to receive a Pediatric Review Voucher from the FDA upon approval. The FDA has granted iopofosine I 131 Breakthrough, six Orphan Drug, four Rare Pediatric Drug and two Fast Track Designations for various cancer indications, and the EMA has granted iopofosine I 131 PRIority MEdicines (PRIME) designation.

Cellectar is also developing CLR 121125 (CLR 125), an iodine-125 Auger-emitting program targeted for solid tumors, such as triple negative breast (TNBC), lung, and colorectal cancer, and is currently being evaluated in a Phase 1b study for TNBC, which will determine the recommended dose for the subsequent Phase 2 trial. CLR 125 has been well tolerated in vivo and has demonstrated strong preclinical data showing reduction or inhibition of solid tumor growth.

In addition to these assets, the Cellectar team is developing CLR 121225 (CLR 225), an actinium-225 based program targeting solid tumors in indications with significant unmet need, such as pancreatic cancer, as well as proprietary preclinical PDC chemotherapeutic programs and multiple partnered PDC assets.

For more information, please visit https://www.cellectar.com/ or join the conversation by liking and following us on the company’s social media channels: X, LinkedIn, and Facebook.

Forward Looking Statements Disclaimer
This news release contains forward-looking statements. You can identify these statements by our use of words such as "may," "expect," "believe," "anticipate," "intend," "could," "estimate," "continue," "plans," or their negatives or cognates. These statements are only estimates and predictions and are subject to known and unknown risks and uncertainties that may cause actual future experience and results to differ materially from the statements made. These statements are based on our current beliefs and expectations as to such future outcomes. Drug discovery and development involve a high degree of risk. Factors that might cause such a material difference include, among others, uncertainties related to the ability to identify suitable collaborators, partners, licensees or purchasers for our product candidates and, if we are able to do so, to enter into binding agreements with regard to any of the foregoing, or to raise additional capital to support our operations, or our ability to fund our operations if we are unsuccessful with any of the foregoing. A complete description of risks and uncertainties related to our business is contained in our periodic reports filed with the Securities and Exchange Commission including our Form 10-K for the quarterly period ended March 31, 2026. These forward-looking statements are made only as of the date hereof, and we disclaim any obligation to update any such forward-looking statements.

INVESTORS:
Anne Marie Fields
Precision AQ
212-362-1200
annemarie.fields@precisionaq.com