Actinium Presents New ATNM-400 Data in KRAS and EGFR Mutant Models at SNMMI 2026 Supporting a Mutation-Agnostic Opportunity In Non-Small Cell Lung Cancer

Rhea-AI Summary

Actinium (NYSE American: ATNM) reported new preclinical data for ATNM-400 in non-small cell lung cancer at SNMMI 2026. ATNM-400 outperformed KRAS inhibitors sotorasib and adagrasib in models and showed strong synergy with EGFR inhibitor osimertinib, achieving complete tumor regression in combination.

ATNM-400’s target is expressed in about 98% of NSCLC tumors and can increase 3.5–3.8x after KRAS inhibitor treatment. According to Actinium, this supports a potential mutation-agnostic backbone role across large EGFR- and KRAS-mutant NSCLC segments.

Positive

• KRAS inhibitors increased ATNM-400 target expression up to 3.5–3.8-fold, enhancing combination activity
• In EGFR-mutant models, ATNM-400 plus osimertinib achieved 107% tumor growth inhibition with 100% cures in mice
• ATNM-400 monotherapy delivered 75% tumor growth inhibition versus 40% for osimertinib in an EGFR-mutant model
• Single-dose ATNM-400 caused 124% and 135% tumor inhibition in a KRAS G13D model with full body-weight recovery
• Target antigen present in approximately 98% of NSCLC tumors and highly expressed in about 70%
• KRAS inhibitor NSCLC segment projected over $5 billion and EGFR-mutant segment over $15 billion in peak sales

Negative

• None.

News Market Reaction – ATNM

-4.92% 2.0x vol

3 alerts

-4.92% Session close to close

+10.3% Peak Tracked

-5.2% Trough Tracked

$38.28M Market Cap

2.0x Rel. Volume

In the Jun 3 session, ATNM declined 4.92%, reflecting a moderate negative market reaction. Argus tracked a peak move of +10.3% during that session. Argus tracked a trough of -5.2% from its starting point during tracking. Our momentum scanner triggered 3 alerts that day, indicating moderate trading interest and price volatility. Trading volume was above average at 2.0x the daily average, suggesting increased trading activity.

Data tracked by StockTitan Argus on the day of publication.

Market Context

This announcement presents extensive preclinical evidence that ATNM-400 achieved strong activity acr...

Analysis

This announcement presents extensive preclinical evidence that ATNM-400 achieved strong activity across EGFR- and KRAS-driven NSCLC models, including up to 107% tumor growth inhibition in combination and target expression in roughly 98% of tumors. The data reinforce a mutation-agnostic strategy aimed at large lung cancer segments. In parallel, investors must consider recent NYSE American listing-standard issues and ongoing net losses. Future milestones around clinical entry, durability of response, and safety in humans will be important markers to track.

Key Figures

NSCLC driver share: 40–50% of NSCLC cases NSCLC incidence share: 85% of >2 million cases Target prevalence: 98% of NSCLC tumors +5 more

8 metrics

NSCLC driver share 40–50% of NSCLC cases Proportion of NSCLC with EGFR or KRAS mutations

NSCLC incidence share 85% of >2 million cases NSCLC share of global annual lung cancer diagnoses

Target prevalence 98% of NSCLC tumors ATNM-400 target antigen presence across NSCLC tumors

High target expression 70% of NSCLC tumors Proportion of NSCLC with high target expression

Target upregulation Up to 3.8-fold increase Adagrasib-induced increase in ATNM-400 target expression

Tumor inhibition combo 107% tumor growth inhibition ATNM-400 plus osimertinib in EGFR-mutant model

Single-dose potency 135% tumor inhibition Higher ATNM-400 dose in KRAS G13D Calu-3 model

TAGRISSO sales $7.3 billion Osimertinib 2025 sales in EGFR-mutant NSCLC segment

Historical Context

5 past events · Latest: Jun 01 (Positive)

Pattern 5 events

Date	Event	Sentiment	24h Move	Catalyst
Jun 01	CMO appointment	Positive	-6.3%	Hired experienced oncology CMO to steer pipeline, including ATNM-400, toward key readouts.
Jun 01	Radiochemistry data	Positive	-6.3%	Presented CAR-optimization data suggesting improved tumor targeting and therapeutic index for Ac-225 agents.
May 29	Patents & listing notice	Negative	-6.3%	Announced new patents alongside disclosure of NYSE American equity non-compliance and related timelines.
May 29	ATNM-400 SNMMI preview	Negative	-6.3%	Outlined ATNM-400 poster plans and separately detailed NYSE American listing standards deficiency notice.
May 06	SNMMI abstracts	Positive	-1.6%	Announced three SNMMI 2026 abstracts featuring ATNM-400 in NSCLC and prostate cancer and CAR optimization.

24h Move is the share-price change in the day after each event; other market factors may also have contributed.

Pattern Detected

Recent history shows negative price reactions even to seemingly constructive pipeline and leadership news, while listing-standard issues have coincided with downside as well.

Recent Company History

Over the past month, Actinium highlighted multiple developments around its radioconjugate platform. The company previewed and then delivered SNMMI 2026 presentations, including new ATNM-400 data across NSCLC and other tumors, yet shares fell about 6.35% following several of these updates. A listing-standards notice from NYSE American underscored balance sheet pressure. The appointment of a new Chief Medical Officer on Jun 1 and additional radiochemistry data reinforced the pipeline focus. Today’s ATNM-400 NSCLC data deepen this same narrative of broad, mutation-agnostic potential within solid tumors.

Key Terms

non-small cell lung cancer, kras, braf, radioconjugate, +2 more

6 terms

non-small cell lung cancer medical

"presented new preclinical data on ATNM-400 in non-small cell lung cancer (NSCLC)"

A broad category of lung tumors that grow from the cells lining the airways and make up the majority of lung cancer cases; it includes several subtypes that behave and respond to treatment differently, like different models of the same car family. It matters to investors because its large patient population and variety of treatment options — surgery, traditional chemo, targeted drugs and immunotherapies — create major markets where clinical trial results, drug approvals or changing treatment guidelines can quickly affect a company’s revenue and stock value.

kras medical

"EGFR, KRAS, BRAF, ALK and others, each marketed by different companies"

KRAS is a gene that makes a protein acting like a switch to control cell growth; certain changes (mutations) can lock that switch on and drive uncontrolled cell multiplication, which is a common cause of many cancers. Investors care because drugs or tests targeting KRAS mutations can create large markets or avoidable risks depending on trial results and regulatory decisions, much like a key product feature deciding a gadget’s commercial success.

braf medical

"EGFR, KRAS, BRAF, ALK and others, each marketed by different companies"

BRAF is a human gene that produces a protein acting like an on/off switch for cell growth; certain mutations let that switch stay stuck in the “on” position, which can drive uncontrolled cell division in many cancers. Investors care because tests that find BRAF mutations and drugs that target them can change treatment decisions, win regulatory approvals, and create revenue streams for biotech and diagnostics companies—similar to finding a key that unlocks a specific therapy market.

radioconjugate medical

"ATNM-400 is a radioconjgate comprising an antibody coupled to Actinium-225"

A radioconjugate is a medicine made by attaching a small amount of radioactive material to a targeting molecule so the radiation is delivered directly to specific cells, like a guided missile carrying a tiny explosive to a precise address. Investors care because its safety, effectiveness, manufacturing complexity, and regulatory path determine development costs, market size and reimbursement potential, affecting a company’s future revenue and risk profile.

actinium-225 medical

"Actinium's first-in-class Actinium-225 (Ac-225) antibody radioconjugate"

Actinium-225 is a rare, radioactive form of the metal actinium used as a microscopic radiation source in some cancer treatments; it emits very strong, short-range radiation that can destroy diseased cells when attached to a carrier drug. Investors pay attention because supply is limited and production is complex, so shortages or cost changes can directly affect the development, manufacturing and valuation of companies pursuing therapies that rely on this scarce medical “fuel.”

pet imaging medical

"In a KRAS G12C model (NCI-H358), PET imaging of radiolabeled ATNM-400 showed"

PET imaging is a noninvasive medical scan that works like a molecular camera, using tiny radioactive tracers to reveal biological activity inside the body—for example metabolism, blood flow, or the presence of specific proteins. It matters to investors because PET results guide diagnosis, show whether a drug reaches its intended target and how patients respond, and therefore affect clinical trial success, regulatory approval, reimbursement decisions and demand for scanners, tracers and related services.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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• New KRAS-mutant data show ATNM-400 outperformed standard-of-care inhibitors sotorasib and adagrasib as a monotherapy. Treatment with these agents increased expression of the ATNM-400 target greater than 3.5x and enhanced their effect in combination
   
• Additional data in the EGFR-mutant setting demonstrated powerful synergy with osimertinib due to enhanced target expression in treated animals resulting in complete tumor regression in the combination arm
   
• The data with EGFR and KRAS mutations which account for approximately 40-50 percent of all NSCLC cases provide compelling evidence of the potential of ATNM-400 as a monotherapy or in combination with inhibitory agents against these mutations
   
• ATNM-400 is a radioconjgate comprising an antibody coupled to Actinium-225 which causes cell death via double stranded DNA breaks independent of cellular mechanisms and offers broad potential as a mutation agnostic agent in NSCLC where its target is expressed in over 90 percent of tumors with greater expression as resistance emerges

NEW YORK, June 3, 2026 /PRNewswire/ -- Actinium Pharmaceuticals, Inc. (NYSE American: ATNM) (Actinium or the Company), a pioneer in the development of targeted radiotherapies, on June 2, 2026, presented new preclinical data on ATNM-400 in non-small cell lung cancer (NSCLC) at the Society of Nuclear Medicine and Molecular Imaging (SNMMI) 2026 Annual Meeting in Los Angeles, California.

The new KRAS-mutant data, together with a growing body of EGFR-mutant data, demonstrate ATNM-400's activity across the two major mutation driver classes in NSCLC and support a distinct strategic opportunity. ATNM-400 can be developed as a potential mutation-agnostic backbone for the broader NSCLC market, alone or in combination with standard-of-care therapies, rather than as another mutation-specific drug for a narrow subset.

NSCLC accounts for roughly 85% of the more than two million lung cancer cases diagnosed globally each year, a market more than twice the size of prostate cancer. It is also highly heterogeneous: no single mutation dominates, so treatments are fragmented across mutation-specific therapies such as EGFR, KRAS, BRAF, ALK and others, each marketed by different companies, each addressing only a molecular subset, and each ultimately limited by acquired resistance. ATNM-400, Actinium's first-in-class Actinium-225 (Ac-225) antibody radioconjugate, is designed to break out of that single-mutation paradigm. Rather than blocking a specific mutant protein, it delivers a high-linear-energy-transfer alpha-particle payload that induces dense, irreversible double-strand DNA breaks and tumor-cell death independent of a tumor's driver mutation or signaling pathway, the mechanistic basis of its mutation-agnostic activity.

ATNM-400's target antigen, from previously published immunohistochemistry studies, is present in approximately 98% of NSCLC tumors and highly expressed in approximately 70% of those tumors. It is conserved across EGFR-, KRAS-, and other driver-defined subgroups, and further increased in tumors that have become resistant to EGFR, KRAS, and immune-checkpoint therapies. In new KRAS-mutant studies presented at SNMMI, sotorasib (active ingredient in LUMAKRAS^®/Amgen) and adagrasib (active ingredient in KRAZATI^®/BMS) increased ATNM-400's target up to 3.5- and 3.8-fold, respectively, and adding ATNM-400 deepened tumor-cell killing beyond either inhibitor alone. These results demonstrate the same target-expression increasing, synergy-enabling biology shown previously with the EGFR inhibitor osimertinib, which produced tumor growth inhibition of 107% when combined with ATNM-400.

These combination benefits also broaden ATNM-400's commercial opportunity. The franchises it could enhance are substantial; the KRAS inhibitor class in NSCLC is projected to exceed $5 billion in peak sales, and the EGFR-mutant segment has peak sales estimates over $15 billion, led by osimertinib (active ingredient in TAGRISSO^®/AZ), which generated $7.3 billion in 2025. This positions ATNM-400 to participate in these established markets by enhancing the standard of care, while also reaching the broader NSCLC population beyond any single mutation.

Sandesh Seth, Actinium's Chairman and CEO, said, "Today's data further strengthen our conviction that ATNM-400 represents a fundamentally different approach to treating NSCLC solid tumors. While most targeted therapies are designed for a single mutation-defined patient population, ATNM-400 combines the mutation-independent cell-killing power of Actinium-225 with a target that is broadly expressed across tumors and becomes even more abundant as resistance emerges. The consistency of activity we have now demonstrated across both EGFR- and KRAS-driven NSCLC supports our vision for ATNM-400 as a potential mutation-agnostic backbone therapy that can be used alone or in combination across large patient populations. We believe this opportunity could extend beyond lung cancer and may position ATNM-400 as a foundational therapy across multiple solid tumor indications."

Highlights from the SNMMI 2026 Poster Presentation

Poster Titled: ATNM-400: A First-in-Class Actinium-225 Antibody Radioconjugate Demonstrating Durable, Mutation-Agnostic Anti-Tumor Activity in Non-Small Cell Lung Cancer Models

New data demonstrated ATNM-400's potential as a mutation-agnostic antibody radioconjugate therapy for NSCLC:

• Across a panel of four lung cancer cell lines spanning EGFR- and KRAS-driver mutations, ATNM-400 bound and was internalized specifically by the three target-positive lines (NCI-H1975, NCI-H358 and Calu-3) but not by the target-negative line (A549), confirming that its activity is driven by target expression rather than by any particular mutation.

• In a KRAS G12C model (NCI-H358), PET imaging of radiolabeled ATNM-400 showed the drug concentrating in the tumor with low uptake in healthy tissue, visually confirming that it reaches its target in a living animal and delivers its alpha payload where intended while largely sparing normal organs.

• In a KRAS G13D model (Calu-3), a single dose of ATNM-400 drove tumor regression (124% and 135% inhibition at two dose levels), indicating marked antitumor potencywith full body-weight recovery. Deep responses from one dose with a clean tolerability profile point to a wide therapeutic window and dosing flexibility, favorable attributes for clinical translation.

• Treatment with both approved KRAS inhibitors (sotorasib and adagrasib) raised ATNM-400's target expression dose-dependently—up to roughly 3.5- to 3.8-fold—reaching statistical significance at every dose (p < 0.0001). The effect occurred with both agents, indicating a class-wide consequence of KRAS G12C inhibition that builds a rationale for combining ATNM-400 with these therapies.

• ATNM-400 plus sotorasib or adagrasib decreased cancer-cell viability beyond either inhibitor alone. The data demonstrate that ATNM-400 has development potential not only as a monotherapy but also in combination with these leading KRAS therapies and possibly the entire KRAS-mutant class.

• In an EGFR-mutant model (NCI-H1975), ATNM-400 monotherapy achieved 75% tumor growth inhibition versus 40% for osimertinib; combined with osimertinib it reached 107% inhibition with complete cures in 100% of mice. Osimertinib raised target expression, providing a clear rationale for the combination.

About Actinium Pharmaceuticals, Inc.

Actinium is a pioneer in targeted radiotherapies designed to improve outcomes for patients with cancer. The company employs a biology-driven approach to develop differentiated radiopharmaceuticals for solid tumors and hematologic malignancies. Its mission is to transform cancer treatment through innovative radioconjugates that maximize therapeutic efficacy while minimizing toxicity to healthy tissue by combining expertise in tumor biology, translational medicine, and radiochemistry. Since inception, Actinium has focused on developing innovative radiotherapies. Its pipeline reflects this strategy across three areas: (1) solid tumor therapeutics including ATNM-400 and Actimab-A with pan-tumor potential; (2) Actimab-A as a therapeutic backbone for acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) in collaboration with the National Cancer Institute (NCI); and (3) targeted conditioning agents including Iomab-B for bone marrow transplant and Iomab-ACT for cell and gene therapy conditioning. ATNM-400 targets a novel antigen distinct from PSMA and has demonstrated preclinical activity across metastatic castration-resistant prostate cancer (mCRPC), non-small cell lung cancer (NSCLC), and breast cancer. Actimab-A has shown improved survival in relapsed/refractory AML with CLAG-M and is advancing toward a Phase 2/3 trial, with additional development ongoing through a CRADA with the NCI. Actinium is also advancing preclinical solid tumor programs and holds approximately 250 patents and patent applications, including intellectual property related to cyclotron-based production of Ac-225. For more information, please visit www.actiniumpharma.com.

Forward-Looking Statements

This press release may contain projections or other "forward-looking statements" within the meaning of the "safe-harbor" provisions of the private securities litigation reform act of 1995 regarding future events or the future financial performance of the Company which the Company undertakes no obligation to update. These statements, including statements as related to regaining compliance with the rules of the NYSE American and submission of a compliance plan, are based on management's current expectations and are subject to risks and uncertainties that may cause actual results to differ materially from the anticipated or estimated future results, including the risks and uncertainties associated with preliminary study results varying from final results, estimates of potential markets for drugs under development, clinical trials, actions by the FDA and other governmental agencies, regulatory clearances, responses to regulatory matters, the market demand for and acceptance of Actinium's products and services, performance of clinical research organizations and other risks detailed from time to time in Actinium's filings with the Securities and Exchange Commission (the "SEC"), including without limitation its most recent annual report on Form 10-K, subsequent quarterly reports on Forms 10-Q and Forms 8-K, each as amended and supplemented from time to time.

Investors: investorrelations@actiniumpharma.com

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SOURCE Actinium Pharmaceuticals, Inc.

FAQ

What did Actinium (ATNM) announce about ATNM-400 data on June 3, 2026?

Actinium announced new preclinical ATNM-400 data in non-small cell lung cancer models, presented at SNMMI 2026. According to Actinium, results showed strong activity in KRAS- and EGFR-mutant settings, supporting ATNM-400 as a potential mutation-agnostic backbone therapy.

How did ATNM-400 perform versus sotorasib and adagrasib in KRAS-mutant NSCLC models for ATNM (ATNM-400)?

ATNM-400 outperformed standard-of-care KRAS inhibitors sotorasib and adagrasib as monotherapy in KRAS-mutant models. According to Actinium, both inhibitors increased ATNM-400’s target expression up to 3.5–3.8-fold and combinations further reduced cancer-cell viability beyond either inhibitor alone.

What were the ATNM-400 and osimertinib combination results in EGFR-mutant NSCLC models for ATNM stock?

ATNM-400 plus EGFR inhibitor osimertinib achieved 107% tumor growth inhibition with complete cures in 100% of mice. According to Actinium, ATNM-400 alone reached 75% inhibition versus 40% for osimertinib, and osimertinib increased ATNM-400 target expression, supporting combination development.

Why is ATNM-400 described as a potential mutation-agnostic therapy in NSCLC for Actinium (ATNM)?

ATNM-400 delivers an Actinium-225 alpha payload causing double-strand DNA breaks independent of driver mutation. According to Actinium, its target antigen appears in about 98% of NSCLC tumors and remains conserved across EGFR-, KRAS-, and other subgroups, including resistant tumors.

What market opportunity does Actinium see for ATNM-400 in KRAS and EGFR-mutant NSCLC segments (ATNM)?

Actinium links ATNM-400 to enhancing major KRAS and EGFR inhibitor franchises in NSCLC. According to Actinium, the KRAS inhibitor class is projected above $5 billion peak sales and EGFR-mutant NSCLC over $15 billion, with osimertinib generating $7.3 billion in 2025.

What preclinical safety and targeting signals were reported for ATNM-400 by Actinium (NYSE American: ATNM)?

In KRAS G13D models, single-dose ATNM-400 caused strong tumor regression with full body-weight recovery, and PET imaging showed tumor-focused uptake. According to Actinium, these data support a wide therapeutic window and precise tumor targeting while largely sparing normal organs in animals.