Cellectar Enrolls First Patient in CLR 125 Auger-Emitting Radioconjugate Phase 1b Clinical Trial Targeting Refractory Triple Negative Breast Cancer (TNBC)
Rhea-AI Summary
Cellectar (NASDAQ: CLRB) enrolled the first patient in a Phase 1b trial of CLR 125 for relapsed or refractory triple negative breast cancer (TNBC) on April 14, 2026. The open-label, dose-escalation study will test three dose regimens and image tumor uptake to inform a recommended Phase 2 dose.
Preclinical data showed selective tumor uptake and no observed end-organ or hematologic toxicity at evaluated doses; additional sites are planned to activate in Q2 with dosimetry, safety, and efficacy updates during 2026.
Positive
- First patient enrolled in Phase 1b on April 14, 2026
- Three defined dose regimens: 32.75, 62.5, 95 mCi
- Preclinical selective tumor uptake with no observed organ toxicity
- Planned site activations in Q2 2026 and program updates during 2026
Negative
- Phase 1b early stage — clinical efficacy unproven
- Approximately 15 patients per arm limits statistical power
- No reported human safety or efficacy readouts yet
News Market Reaction – CLRB
On the day this news was published, CLRB gained 7.66%, reflecting a notable positive market reaction. This price movement added approximately $827K to the company's valuation, bringing the market cap to $11.62M at that time.
Data tracked by StockTitan Argus on the day of publication.
Key Figures
Market Reality Check
Peers on Argus
CLRB slipped 0.72% while peers showed mixed moves: EDSA +6.5%, THAR +5.8%, PULM +0.83%, LSTA -0.2%, SYBX flat. Momentum scanner flagged PULM up and COCP down, confirming stock-specific dynamics rather than a broad sector rotation.
Previous Clinical trial Reports
| Date | Event | Sentiment | Move | Catalyst |
|---|---|---|---|---|
| Oct 14 | Preclinical data update | Positive | +1.6% | Promising preclinical CLR 225 pancreatic cancer data at AACR conference. |
| Jun 24 | Trial protocol submitted | Positive | +8.6% | FDA submission of Phase 1b CLR 125 protocol for TNBC. |
| Jun 11 | Phase 1 trial update | Positive | +16.6% | Promising CLOVER‑2 iopofosine I 131 data in pediatric glioma. |
| Dec 10 | Strategic pipeline update | Negative | -76.2% | Refocus on radioconjugates and ~60% headcount reduction in restructuring. |
| Jul 23 | Pivotal WM results | Positive | -18.5% | Iopofosine I 131 exceeded primary endpoint in WM pivotal study. |
Across five tagged clinical-trial headlines, CLRB has shown large but mixed reactions, with 4 aligned moves and 1 divergence and an average move of -13.57%, including one sharp selloff on a restructuring update.
Recent clinical and pipeline news for Cellectar shows a shift toward its radioconjugate platform. In July 2024, iopofosine I 131 exceeded pivotal Waldenström macroglobulinemia endpoints, yet shares fell. By December 2024, a strategic update and 60% headcount reduction drove a steep decline. Through 2025, the company highlighted positive pediatric glioma data, progress on CLR 225, and, in June 2025, FDA submission of the CLR 125 Phase 1b TNBC protocol. Today’s first‑patient enrollment concretely advances that same CLR 125 program.
Historical Comparison
Over the last five clinical‑trial headlines, CLRB’s average move was -13.57%. Today’s first‑patient enrollment in the CLR 125 TNBC Phase 1b trial continues that clinical focus, and any reaction would be judged against this volatile history.
Clinical‑trial news shows progression from pivotal iopofosine I 131 data and restructuring toward early‑stage solid tumor programs, including INDs and protocol submission for CLR 125, now advancing to active Phase 1b enrollment in TNBC.
Market Pulse Summary
The stock moved +7.7% in the session following this news. A strong positive reaction aligns with Cellectar’s pattern of sizable moves on clinical news, where prior tagged events averaged -13.57% but included large upside days. First‑patient enrollment in the CLR 125 TNBC Phase 1b trial marks tangible execution after earlier protocol submission. However, historical restructuring, going‑concern language, and dependence on external financing in filings indicate that clinical momentum must be weighed against balance sheet and dilution risk noted in past disclosures.
Key Terms
auger-emitting radioconjugate medical
iodine-125 medical
iopofosine i 131 medical
biodistribution medical
dosimetry medical
recist medical
progression-free survival medical
triple negative breast cancer medical
AI-generated analysis. Not financial advice.
Study will evaluate tumor-specific uptake, safety, tolerability, and preliminary efficacy signals of CLR 125 in refractory TNBC, to determine recommended Phase 2 dose
FLORHAM PARK, N.J., April 14, 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 the first patient has been enrolled in the Phase 1b trial of CLR 121125 (CLR 125) for the potential treatment of triple negative breast cancer (TNBC).
CLR 125 is Cellectar’s proprietary Auger-emitting radioconjugate incorporating iodine-125 to achieve intracellular delivery and direct DNA-level damage in tumor cells. The molecular structure of CLR 125 is identical to that of iopofosine I 131 (CLR 131) and the demonstrated clinical activity, safety, and tumor-targeting characteristics of iopofosine I 131 provide important validation of the platform and support translational relevance. However, these radioconjugates differ in their radiobiologic behavior at the tumor level, resulting in distinct mechanisms of action and therapeutic profiles. In preclinical studies, CLR 125 showed selective tumor uptake and statistically significant activity in vivo models of TNBC with no observed end-organ or hematologic toxicity at evaluated doses.
“Treating the first patient in this Phase 1b trial is a significant milestone for Cellectar and for those impacted by triple negative breast cancer, a condition still defined by a profound lack of targeted therapies,” said James Caruso, president and chief executive officer of Cellectar. “CLR 125 embodies our commitment to optimize our proprietary PDC delivery platform to develop highly selective radioconjugates capable of delivering precise cytotoxic radiation while minimizing systemic toxicity. With additional study sites being activated in Q2, we are poised to rapidly advance this program and plan to provide dosimetry, safety, and efficacy updates throughout 2026.”
The Phase 1b clinical trial is an open-label, dose-escalation study in patients with relapsed or refractory TNBC, designed to evaluate three dose levels and dosing regimens of CLR 125 (32.75 mCi administered over 4 cycles, 62.5 mCi over 3 cycles, and 95 mCi over 2 cycles), with approximately 15 patients enrolled per treatment arm. The study incorporates imaging-based assessments to characterize tumor uptake and biodistribution, supporting prediction of safety and therapeutic activity. Clinical endpoints include safety and tolerability, as well as preliminary efficacy measures, including tumor response per RECIST criteria and progression-free survival.
About Triple Negative Breast Cancer
Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer characterized by the absence of estrogen receptors, progesterone receptors, and HER2 protein expression. This lack of common therapeutic targets makes TNBC particularly challenging to treat, with limited options beyond chemotherapy. TNBC tends to grow and spread more quickly than other breast cancer types and disproportionately affects younger women and those of African descent. In the U.S., approximately
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.
Additionally, 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 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 year ended December 31, 2025. 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
