Cellectar Advances CLR 125 Into Early Breast Cancer Trial, Adding Depth to Its Radiotherapy Pipeline

Cellectar Biosciences Inc (CLRB) announced an update on their ongoing clinical study.

Cellectar Biosciences is running a Phase 1b study called “A Phase 1b, Open-Label Parallel Study Evaluating CLR 125 in Patients With Relapsed or Refractory Triple Negative Breast Cancer.” The goal is to find a safe and effective dose of CLR 125 for women whose triple negative breast cancer has come back or not responded to treatment. The study focuses on safety, side effects, and early signs of benefit in a hard-to-treat cancer, which makes any positive signal important for future trials and for the company’s long-term value.

The main treatment is CLR 125, an experimental targeted radiation drug given by IV. It is designed to deliver radiation directly to tumor cells while limiting damage to healthy tissue. A smaller group of patients will also receive a one-time dose of Iopofosine I 131 (CLR 131) so researchers can better track how radiation moves through the body and the tumor.

The trial is interventional and randomized, with patients assigned to one of three CLR 125 dose groups in parallel. There is no placebo and no blinding; both doctors and patients know what dose is given. The primary purpose is treatment: to test different dose levels, learn what side effects appear, and decide which dose is best suited to move forward into later-stage studies.

The study is listed as recruiting. It was first submitted in November 2025, signaling when the trial formally entered the regulatory system. The latest update was filed on January 8, 2026, confirming that the protocol and status information are current. Primary and final completion dates are not yet posted, which is typical for an early-stage oncology study still ramping up enrollment.

For investors, the key takeaway is that Cellectar is progressing another targeted radiotherapy asset into the clinic in a difficult cancer setting, adding depth to its pipeline beyond Iopofosine I 131. Continued recruitment and regular updates can support positive sentiment for CLRB, especially if early safety and activity data show a clear path to Phase 2. However, this remains high-risk, early-stage development, and any delay, safety concern, or weak efficacy signal could pressure the stock. The study also sits within a crowded landscape of targeted therapies and antibody-drug conjugates in breast cancer, so investors should track how CLR 125 might differentiate on safety, dosing convenience, or outcomes. The study is currently ongoing and updated, with further details available on the ClinicalTrials.gov portal.

To learn more about CLRB’s potential, visit the Cellectar Biosciences Inc drug pipeline page.