Cellectar Biosciences Reports First Quarter 2026 Financial Results and Provides Corporate Updates

Cellectar Reports Positive Iopofosine I 131 Data and Secures $140M Financing

Cellectar Biosciences announced its Q1 2026 financial results and provided key corporate updates. The company reported positive 12-month follow-on data from its Phase 2b CLOVER-WaM study of iopofosine I 131 in relapsed/refractory Waldenström Macroglobulinemia (r/r WM), showing a 61.8% major response rate and a median duration of response of 17.8 months. This data supports plans for a Phase 3 confirmatory study and accelerated FDA approval. Additionally, Cellectar completed a financing of up to $140 million to fund these initiatives and initiated a Phase 1b study for CLR 125 in triple-negative breast cancer, expanding its radiopharmaceutical pipeline.

• Strong Efficacy Data for Iopofosine I 131 in r/r WM: Cellectar reported positive 12-month follow-up data from the Phase 2b CLOVER-WaM study for iopofosine I 131 in relapsed/refractory Waldenström Macroglobulinemia. The study achieved its primary and secondary endpoints, demonstrating a 61.8% major response rate (MRR) and a median duration of response (DoR) of 17.8 months in the protocol study population (n=55). An overall response rate (ORR) of 83.6% and median progression-free survival (PFS) of 13.5 months were also observed, reinforcing confidence in the drug's potential.
• Significant Financing to Advance Pipeline: The company successfully completed a financing round of up to $140 million, including an upfront payment of approximately $35 million and up to $105 million in milestone-based securities. This capital infusion, led by Nantahala Capital and other healthcare-focused investors, provides the necessary resources to initiate the Phase 3 confirmatory study for iopofosine I 131 in WM, support its U.S. FDA accelerated approval filing, and advance other pipeline programs towards potential commercialization.
• Pipeline Expansion with CLR 125 in TNBC: Cellectar expanded its radioconjugate pipeline by enrolling the first patients in a Phase 1b dose-finding study for CLR 125 in refractory triple-negative breast cancer (TNBC). This initiative addresses a significant unmet medical need in solid tumors. Early dosimetry, safety, and efficacy data for CLR 125 are anticipated mid-year 2026, with additional study sites expected to be activated throughout the second quarter, paving the way for a subsequent Phase 2 trial.
• Regulatory Progress and ASCO Presentation: The positive 12-month follow-up data for iopofosine I 131 aligns with FDA expectations, positioning the company for an accelerated approval submission and the initiation of a Phase 3 confirmatory study. Cellectar is also working with the EMA for a Conditional Marketing Approval. Furthermore, efficacy results from the CLOVER-WaM study, specifically for patients treated immediately post-BTKi therapy, have been selected for presentation at the ASCO 2026 Annual Meeting, highlighting the drug's performance in a challenging patient subset.

Iopofosine I 131's Durable Efficacy in Relapsed/Refractory WM

The ASPEN study (BGB-3111-302), a pivotal phase 3 trial, compared zanubrutinib versus ibrutinib in patients with MYD88-mutated Waldenström macroglobulinemia. This study demonstrated comparable efficacy between the two BTK inhibitors while showing a favorable safety profile for zanubrutinib versus ibrutinib, ultimately leading to zanubrutinib's approval for WM patients. Notably, zanubrutinib showed superior efficacy compared to ibrutinib in WM patients harboring MYD88 wild-type, CXCR4, or TP53 mutations. The long-term extension study (BGB-3111-LTE1) followed 47 patients who transitioned from ibrutinib to zanubrutinib, demonstrating that 85% of patients remained on zanubrutinib treatment at median follow-up of 15.3 months, with disease response maintained or improved in 96% of efficacy-evaluable patients.

An international bendamustine-rituximab study evaluated 253 patients receiving frontline fixed-duration therapy and demonstrated durable efficacy with 5-year progression-free survival of 65% and overall survival of 87% at median follow-up of 5.9 years. The study revealed that while efficacy was similar between MYD88L265P and MYD88 wild-type subcohorts, patients with CXCR4 mutations experienced significantly shorter progression-free survival (median 3.3 versus 8.8 years) and overall survival compared to CXCR4 wild-type patients. Progression of disease within 24 months occurred in 11.5% of patients and was associated with inferior subsequent survival outcomes.

A retrospective study from Jiangsu Province Hospital examined 15 cases of histologic transformation from WM to diffuse large B-cell lymphoma, revealing that patients receiving BTK inhibitor-based regimens after transformation showed significantly prolonged overall survival compared to those who did not receive BTKi therapy. The median overall survival from transformation was 26.0 months, with most cases presenting as non-germinal center B-cell DLBCL and frequent involvement of immune-privileged sites. Additionally, real-world evidence from Finland and Germany demonstrated median overall survival ranging from 7.3 to 7.9 years, with improvements in outcomes observed over recent time periods, likely reflecting advances in targeted therapies and management strategies.

Charting Iopofosine I 131's Path to Accelerated Approval

The iNNOVATE study represents the most pivotal phase III trial in Waldenström macroglobulinemia, featuring a double-blind, randomized, placebo-controlled design that enrolled 150 patients with confirmed symptomatic WM. Patients were randomly assigned to receive either once-daily ibrutinib 420 mg plus rituximab or placebo plus rituximab (75 patients per arm), with eligibility criteria including both previously untreated and previously treated patients who had demonstrated at least a minor response to prior rituximab-based therapy. The study's primary endpoint was progression-free survival, while secondary endpoints encompassed response rate, time to next treatment, hemoglobin improvement, overall survival, and safety parameters. With a median follow-up of 50 months, the trial demonstrated that median PFS was not reached in the ibrutinib-rituximab arm versus 20.3 months with placebo-rituximab, establishing a new standard of care.

The European DRC versus B-DRC randomized study provided critical insights into treatment-naïve WM patients by comparing dexamethasone, rituximab, and cyclophosphamide (DRC) against bortezomib-DRC (B-DRC) across six treatment cycles. This 204-patient study utilized progression-free survival as its primary endpoint, with secondary endpoints including response rates, overall survival, and safety assessments. After a median follow-up of 27.5 months, the estimated 24-month PFS was 80.6% for B-DRC versus 72.8% for DRC, while major responses at treatment completion favored B-DRC (80.6% versus 69.9%). The ZID regimen phase II trial (NCT04463953) evaluated zanubrutinib, ixazomib, and dexamethasone in 27 newly diagnosed WM patients, employing deep remission rate as the primary endpoint through up to six 28-day induction cycles followed by consolidation therapy extending to 24 cycles total.

Additional significant trials include the ASPEN phase III study comparing zanubrutinib versus ibrutinib in patients with mutated MYD88, and the tirabrutinib phase II multicenter study that enrolled 27 patients across treatment-naïve and relapsed/refractory cohorts with major response rate as the primary endpoint. The everolimus trial in relapsed/refractory WM patients demonstrated the importance of mTOR pathway targeting, achieving a 70% overall response rate in 50 treated patients with measurable disease criteria requiring IgM monoclonal protein >1,000 mg/dL and >10% marrow involvement. These diverse study designs collectively establish the therapeutic landscape for WM, spanning from nucleoside analogues like fludarabine to modern targeted therapies, each contributing unique endpoint data that informs current treatment algorithms.

Expanding Cellectar's PDC Platform Beyond Waldenström Macroglobulinemia

Cellectar's iopofosine I 131 (CLR 131) is being investigated across multiple oncology indications beyond Waldenström Macroglobulinemia, spanning both clinical trials and preclinical studies. These investigations utilize various intervention models ranging from single-dose administrations to combination therapies with external beam radiation.

• Head and neck cancer - Phase 1 clinical trial (NCT04105543) combining CLR 131 with reduced-dose external beam radiation therapy (EBRT) in patients with recurrent/metastatic disease who previously received curative intent radiotherapy. The intervention model involves two therapeutic doses of CLR 131 administered on days 1 and 8, followed by EBRT to achieve 60-70 Gy total radiation dose.

• Advanced solid tumors - Multiple Phase 1 studies including a single-injection study of 370 MBq (131)I-CLR1404 in eight patients with refractory or relapsed tumors (NCT00925275), and a Phase 1b adaptive dose-escalation study in ten patients to assess safety and antineoplastic properties. Dose-limiting toxicities of thrombocytopenia and neutropenia were observed at doses ≥31.25 mCi/m².

• Pediatric malignancies - Preclinical studies demonstrate therapeutic potential in neuroblastoma, rhabdomyosarcoma, and Ewing sarcoma using single-dose intravenous injection models. In neuroblastoma xenografts, CLR 124 uptake was 22% higher than I-MIBG in MIBG-avid models, with significant tumor growth delay and extended survival across all pediatric xenograft models tested.

• Brain tumors - Pilot imaging trial in 12 patients using single injection of 185 MBq I-CLR1404 with PET/CT imaging at 6, 24, and 48 hours post-injection. Positive uptake was detected in 9 of 13 lesions, including 5/5 high-grade tumors and 1/2 low-grade tumors.

CLR 131's Momentum: Advancing Radiotheranostics in Hematologic Malignancies and Beyond

The recent announcement from Cellectar Biosciences marks a pivotal moment for the company and the broader field of radiotheranostics, particularly with the compelling 12-month follow-on data for iopofosine I 131 (CLR 131) in relapsed/refractory Waldenström Macroglobulinemia (r/r WM). A major response rate of 61.8% and a median duration of response of 17.8 months in this challenging patient population are highly encouraging, suggesting CLR 131 could offer a much-needed new therapeutic avenue. This robust clinical profile supports the company's strategy for an accelerated FDA approval pathway, which could expedite patient access to this innovative targeted radiopharmaceutical.

The strength of CLR 131 lies in its theranostic nature, utilizing the same phospholipid ether analog scaffold for both diagnostic imaging (CLR 124) and therapeutic delivery (CLR 131). Research indicates that CLR 124 PET imaging can accurately predict CLR 131's 3D therapeutic dosimetry, a critical capability for personalized treatment planning. This advanced dosimetry, often employing Monte Carlo methods, allows for a more precise understanding of dose distribution within tumors and normal tissues, potentially optimizing efficacy while mitigating side effects. This approach has shown promise across various solid tumors, including triple-negative breast cancer, pediatric solid tumors, osteosarcoma, and head and neck cancer, underscoring the platform's broad applicability.

However, as with any novel therapy, certain considerations are paramount:

• Myelosuppression: While generally manageable and transient, Grade 4 hematologic toxicities like leukopenia, thrombocytopenia, and anemia have been observed with CLR 131, particularly in combination with external beam radiation therapy. Careful patient selection and monitoring will be crucial, especially in a heavily pre-treated r/r WM cohort.

• Dosimetry Complexity: The intricacies of radiopharmaceutical dosing and the potential for dose heterogeneity require thorough validation in larger studies to ensure consistent and optimal therapeutic outcomes.

• Regulatory Landscape: Despite the positive data, the historical regulatory environment for radiopharmaceuticals, often characterized by rigid interpretations, could present challenges to the accelerated approval timeline.

The substantial financing secured by Cellectar Biosciences provides a strong foundation to advance CLR 131 through its confirmatory Phase 3 study and to further develop its pipeline, including CLR 125 in TNBC. This strategic investment reflects a growing confidence in the potential of radiotheranostics to address complex tumor microenvironments and deliver precision oncology, positioning the company as a key player in this evolving therapeutic space.