Safety panel backs higher dose in Radiopharm Theranostics (RADX) HER2 trial

Rhea-AI Filing Summary

Radiopharm Theranostics Ltd (RADX) reported that an independent Data Safety and Monitoring Committee recommended advancing its 177Lu-RAD202 Phase 1 ‘HEAT’ clinical trial to Cohort 4 at a higher dose level of 180mCi in patients with HER2-positive advanced solid tumors. This recommendation follows review of safety data and supports the favorable safety profile observed so far. The HEAT study is being conducted at clinical centers across Australia, with the prior dose level of 130mCi announced in April 2026. RAD202 is a proprietary single-domain monoclonal antibody targeting HER2, a validated oncology target, and previously demonstrated clinical proof-of-concept with positive safety and biodistribution in a diagnostic study involving ten HER2-positive breast cancer patients.

Key Figures

Next dose level: 180mCi Previous dose level: 130mCi Patients in prior diagnostic study: 10 HER2-positive breast cancer patients +1 more

4 metrics

Next dose level 180mCi Cohort 4 dose level in 177Lu-RAD202 Phase 1 HEAT trial

Previous dose level 130mCi Prior dose level in the same Phase 1 HEAT trial announced 8 April 2026

Patients in prior diagnostic study 10 HER2-positive breast cancer patients RAD202 diagnostic study showing clinical proof-of-concept and positive safety and biodistribution

Clinical trials in pipeline 1 Phase 2 and 5 Phase 1 trials Radiopharm clinical program across various solid tumor cancers

Key Terms

Data Safety and Monitoring Committee, biodistribution, single-domain monoclonal antibody, HER2-positive advanced solid tumors, +1 more

5 terms

Data Safety and Monitoring Committee medical

"received a positive recommendation from the Data Safety and Monitoring Committee"

An independent panel of experts that regularly reviews patient safety data and trial results during a clinical study to protect participants and ensure the study is producing reliable information. Like impartial referees who can pause, modify, or stop a trial if safety concerns or clear benefits appear, their findings can alter a drug or device’s development timeline, regulatory prospects, and investor risk, so their assessments matter for company value and timelines.

biodistribution medical

"demonstrated clinical proof-of-concept and had positive safety and biodistribution"

Biodistribution is the map of where a drug, vaccine, or diagnostic agent travels and accumulates inside the body after administration. Investors care because where a product ends up affects how well it works, what side effects it may cause, and whether regulators will approve it—similar to tracking dye in a plumbing system to find leaks or blockages; unexpected destinations can raise safety, cost, and market-adoption risks.

single-domain monoclonal antibody medical

"RAD202 is a proprietary single-domain monoclonal antibody (sdAb)"

A single-domain monoclonal antibody is a small, lab-made protein that binds to one specific part of a single target molecule, like a tiny key made to fit one lock. Because it is smaller and simpler than traditional antibodies, it can reach tight spaces on a target and be cheaper to produce, so its specificity, manufacturability, and clinical effects are key factors investors watch when assessing therapeutic potential and commercial value.

HER2-positive advanced solid tumors medical

"Phase 1 ‘HEAT’ clinical trial in patients with HER2-positive advanced solid tumors"

radiopharmaceuticals medical

"developing innovative oncology radiopharmaceuticals for areas of high unmet medical need"

Radiopharmaceuticals are medicines that carry tiny amounts of radioactive material to help doctors see or treat disease inside the body, acting like a tracer dye for imaging or a microscopic guided missile for targeted therapy. They matter to investors because their safety, regulatory approval, production complexity, short shelf life and hospital reimbursement determine how quickly they can reach patients and generate revenue, affecting a company’s sales potential and risk profile.

FAQ

What did Radiopharm Theranostics (RADX) announce about the RAD202 Phase 1 HEAT trial?

Radiopharm Theranostics announced a positive recommendation from the Data Safety and Monitoring Committee to advance its 177Lu-RAD202 Phase 1 HEAT trial to Cohort 4 at a 180mCi dose in HER2-positive advanced solid tumor patients, following review of safety data.

What dose level is Radiopharm Theranostics (RADX) moving to in the RAD202 HEAT trial?

Radiopharm Theranostics is advancing RAD202 dosing to 180mCi in Cohort 4 of the Phase 1 HEAT trial. The previous reported dose level was 130mCi, reflecting stepwise escalation in HER2-positive advanced solid tumor patients in Australia.

What prior clinical evidence supports RAD202 for Radiopharm Theranostics (RADX)?

A prior diagnostic study in ten HER2-positive breast cancer patients demonstrated clinical proof-of-concept for RAD202, with positive safety and biodistribution. This earlier evidence supports ongoing therapeutic dose-escalation in the Phase 1 HEAT trial for advanced solid tumors.

What is 177Lu-RAD202 being developed for by Radiopharm Theranostics (RADX)?

177Lu-RAD202 is being developed as a radiotherapeutic targeting HER2-positive advanced solid tumors. It is a proprietary single-domain monoclonal antibody designed to deliver lutetium-177 radiation to HER2-overexpressing cancers, including breast and other solid tumors.

Where is the RAD202 Phase 1 HEAT trial being conducted for Radiopharm Theranostics (RADX)?

The Phase 1 HEAT clinical trial of 177Lu-RAD202 is being conducted at clinical centers across Australia. The company previously announced the 130mCi dose level in April 2026 and is now progressing to 180mCi following DSMC review.

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Form 6-K: How Foreign Companies Report to the SEC →

Available on EDGAR 08/20/2026 - 08:00 AM Accepted by SEC EDGAR 08/20/2026 - 08:00 AM Learn about SEC filing dates

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16 UNDER

THE SECURITIES EXCHANGE ACT OF 1934

For the Month of August 2026

Commission File Number: 001-41621

RADIOPHARM THERANOSTICS LIMITED

(Name of Registrant)

Level 3, 62 Lygon Street, Carlton South, Victoria, 3053, Australia

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F ☒       Form 40-F ☐

RADIOPHARM THERANOSTICS LIMITED

EXPLANATORY NOTE

Radiopharm Theranostics Limited (the “Company”) published one announcement (the “Public Notice”) to the Australian Securities Exchange on August 20, 2026 titled:

“RAD advances to Cohort 4 in 177Lu-RAD202 Phase 1 HEAT Trial”

A copy of the Public Notice is attached as an exhibit to this report on Form 6-K.

This Form 6-K, including the exhibits hereto, is incorporated by reference into the registration statement of the Company on Form F-3 (File No. 333-292178) and forms part thereof to the extent not superseded by documents or reports subsequently filed by the Company under the Securities Act of 1933 or the Securities Exchange Act of 1934.

1

EXHIBITS

Exhibit Number		Description
99.1		RAD advances to Cohort 4 in 177Lu-RAD202 Phase 1 HEAT Trial

2

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

	RADIOPHARM THERANOSTICS LIMITED
Date: August 20, 2026	By:	/s/ Amritha Sushil
		Amritha Sushil
		Company Secretary

3

Exhibit 99.1

ASX ANNOUNCEMENT August 20, 2026

Radiopharm Theranostics Receives Positive Recommendation from Data Safety and Monitoring Committee to Advance to Cohort 4 in 177Lu-RAD202 Phase 1 HEAT Clinical Trial

Advancing RAD202 Phase 1 trial to next dose level of 180mCi in patients with HER2+ advanced solid tumors

Previous diagnostic study of RAD202 in ten HER2-positive breast cancer patients demonstrated clinical proof-of-concept with positive safety and biodistribution

Sydney, Australia – 20 August 2026 – Radiopharm Theranostics (ASX: RAD, Nasdaq: RADX, “Radiopharm” or the “Company”), a clinical-stage biopharmaceutical company focused on developing innovative oncology radiopharmaceuticals for areas of high unmet medical need, today announced that it has received a positive recommendation from the Data Safety and Monitoring Committee (DSMC) to advance its clinical-stage radiotherapeutic asset, 177Lu-RAD202 (RAD202), to the next dose level of 180mCi in the Phase 1 ‘HEAT’ clinical trial in patients with Human Epidermal Growth Factor Receptor 2 (HER2)-positive advanced solid tumors¹. The DSMC is a multidisciplinary committee that conducts detailed reviews of study data, discusses potential safety events and provides recommendations regarding trial continuation.

“Advancing RAD202 into Cohort 4 marks a significant step forward in the development of one of our most promising therapeutic candidates,” said Riccardo Canevari, CEO and Managing Director of Radiopharm Theranostics. “The DSMC’s recommendation supports the favorable safety profile observed to date and allows us to continue evaluating higher dose levels in patients with HER2-positive advanced solid tumors. As we execute on our clinical development strategy, we remain focused on unlocking the full potential of RAD202 and generating meaningful data that could support a differentiated radiotherapeutic option for HER2-positive patients in need of new treatment alternatives.”

The Phase 1 ‘HEAT’ study is currently being conducted at clinical centers across Australia. The announcement of the previous dose level in this study of 130mCi was released on 8 April 2026.

About 177Lu-RAD202:

RAD202 is a proprietary single-domain monoclonal antibody (sdAb) that targets the Human Epidermal Growth Factor Receptor 2 (HER2)-positive expression in advanced solid tumors. HER2 is overexpressed in breast cancer and several other solid tumors and represents a validated target in oncology. In a previous diagnostic study of ten HER2-positive breast cancer patients, RAD202 demonstrated clinical proof-of-concept and had positive safety and biodistribution.

¹ clinicaltrials.gov/study/NCT06824155

Radiopharm Theranostics Limited
Suite 1, Level 3, 62 Lygon Street, Carlton South VIC 3053 Australia
ABN: 57 647 877 889

ASX ANNOUNCEMENT August 20, 2026

About Radiopharm Theranostics

Radiopharm Theranostics is a clinical stage radiotherapeutics company developing a world-class platform of innovative radiopharmaceutical products for diagnostic and therapeutic applications in areas of high unmet medical need. Radiopharm is listed on ASX (RAD) and on NASDAQ (RADX). The company has a pipeline of distinct and highly differentiated platform technologies spanning peptides, small molecules and monoclonal antibodies for use in cancer. The clinical program includes one Phase 2 and five Phase 1 trials in a variety of solid tumor cancers including lung, breast, prostate and brain. Learn more at radiopharmtheranostics.com.

Authorized on behalf of the Radiopharm Theranostics Board of Directors by Executive Chairman Paul Hopper.

For more information:

Investors:

Riccardo Canevari

CEO & Managing Director

P: +1 862 309 0293

E: rc@radiopharmtheranostics.com

Anne Marie Fields

Precision AQ (formerly Stern IR)

E: annemarie.fields@precisionaq.com

Media:

Matt Wright

NWR Communications

P: +61 451 896 420

E: matt@nwrcommunications.com.au

Follow Radiopharm Theranostics:

Website – https://radiopharmtheranostics.com/
X – https://x.com/TeamRadiopharm
LinkedIn – https://www.linkedin.com/company/radiopharm-theranostics/

InvestorHub – https://investorhub.radiopharmtheranostics.com/

Radiopharm Theranostics Limited
Suite 1, Level 3, 62 Lygon Street, Carlton South VIC 3053 Australia
ABN: 57 647 877 889

Filing Exhibits & Attachments

1 document

Press Releases

• EX-99.1 RAD ADVANCES TO COHORT 4 IN 177LU-RAD202 PHASE 1 HEAT TRIAL 12.1 KB