Cellectar Enrolls First Patient in CLR 125 Clinical Trial for Refractory Triple Negative Breast Cancer

Study will evaluate tumor-specific uptake, safety, tolerability, and preliminary efficacy of CLR 125 radioconjugate in TNBC patients

Apr. 14, 2026 at 12:52pm

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A translucent X-ray photograph showing the intricate internal structure of a breast tumor, glowing with a faint blue-green bioluminescent energy, conceptually representing a new targeted cancer treatment approach.A novel radioconjugate therapy aims to precisely target and damage triple negative breast cancer tumors while minimizing systemic toxicity.Florham Park Today

Cellectar Biosciences, Inc. has announced that the first patient has been enrolled in the Phase 1b clinical trial of CLR 125, the company's proprietary Auger-emitting radioconjugate, for the potential treatment of refractory triple negative breast cancer (TNBC). The trial is designed to evaluate three dose levels and dosing regimens of CLR 125, with approximately 15 patients enrolled per treatment arm. Clinical endpoints include safety, tolerability, and preliminary efficacy measures.

Why it matters

TNBC is an aggressive subtype of breast cancer with limited treatment options beyond chemotherapy. With a high recurrence rate and poor prognosis, there is a critical need for innovative, targeted therapies to improve outcomes for TNBC patients. CLR 125 represents a novel approach using Cellectar's proprietary PDC delivery platform to selectively target and damage tumor cells while minimizing systemic toxicity.

The details

The Phase 1b clinical trial of CLR 125 is an open-label, dose-escalation study in patients with relapsed or refractory TNBC. The study will evaluate three dose levels and dosing regimens of CLR 125 (32.75 mCi over 4 cycles, 62.5 mCi over 3 cycles, and 95 mCi over 2 cycles), with approximately 15 patients enrolled per treatment arm. The trial incorporates imaging-based assessments to characterize tumor uptake and biodistribution, supporting prediction of safety and therapeutic activity.

  • The first patient has been enrolled in the Phase 1b trial of CLR 125.
  • Additional study sites are being activated in Q2 2026.

The players

Cellectar Biosciences, Inc.

A late-stage clinical biopharmaceutical company focused on the discovery and development of drugs for the treatment of cancer.

James Caruso

President and chief executive officer of Cellectar Biosciences.

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What they’re saying

“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.”

— James Caruso, President and chief executive officer

What’s next

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The takeaway

This clinical trial of CLR 125 represents an important step in the development of a novel, targeted therapy for the treatment of refractory triple negative breast cancer, a disease with significant unmet medical need.