RADX 0001213900-26-044334 6-K Filing: Apr 16, 2026

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 April 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 ☐

Indicate by check mark whether by furnishing the information contained in this Form, the registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes ☐ No ☒

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b): 82-

RADIOPHARM THERANOSTICS LIMITED

EXPLANATORY NOTE

Radiopharm Theranostics Limited (the “Company”) published one announcement (the “Public Notice”) to the Australian Securities Exchange on April 16, 2026 titled:

“RAD Completes Enrollment in Phase 2b Trial of RAD 101”

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

This report on Form 6-K (including the exhibit hereto) shall not be deemed to be “filed” for purposes of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) and shall not be incorporated by reference into any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

EXHIBITS

Exhibit <br><br>Number	Description
99.1	RAD Completes Enrollment in Phase 2b Trial of RAD 101

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: April 16, 2026	By:	/s/ Phillip Hains
		Phillip Hains
		Company Secretary

Exhibit 99.1

ASX ANNOUNCEMENT<br><br> <br>16 APRIL 2026

RadiopharmTheranostics Completes Enrollment in U.S. Phase 2b Imaging Trial of RAD 101 for Diagnosis of Brain Metastases

Interim data to date showed 90% concordancewith MRI (the primary endpoint)

Clinical trial readout (Primary endpoint)expected in June 2026

Plans to advance RAD 101 into U.S.Phase 3 pivotal trial

Sydney, Australia – 16 April 2026 – Radiopharm Theranostics (ASX:RAD, “Radiopharm” or the “Company”), a clinical-stage biopharmaceutical company focused on developing innovative oncology radiopharmaceuticals for areas of high unmet medical needs, today announced that the final patient has been dosed in the U.S. Phase 2b imaging trial (NCT06777433) evaluating RAD 101 in individuals with confirmed recurrent brain metastases from solid tumors of different origins.

“Dosing the final patient in our most advanced diagnostic program represents an important milestone for Radiopharm and underscores the continued momentum of our radiopharmaceutical pipeline,” said Riccardo Canevari, CEO and Managing Director of Radiopharm Theranostics. “The interim results we have seen to date, demonstrating a high level of concordance with MRI, reinforce our confidence in RAD 101’s potential to address a critical unmet need in the accurate detection of recurrent brain metastases. As we look ahead to the full data readout in June, we are focused on advancing this important program into U.S. pivotal trial and initiating constructive dialogue with the FDA to define the optimal regulatory pathway. We believe RAD 101 has the potential to meaningfully improve clinical decision-making for patients and physicians navigating this challenging disease.”

“I would like to take the opportunity to thank all the patients, families, and caregivers for their trust in our clinical trial. The investigators and the Clinical Center did an amazing job in the recruitment process, and our congratulations go to BAMF HEALTH for leading the table of the top recruiters,” added Mr. Canevari.

RAD 101 is the Company’s novel imaging small molecule that targets fatty acid synthase (FASN), a multi-enzyme protein that catalyses fatty acid synthesis and is overexpressed in many solid tumors, including cerebral metastasis. Targeting FASN activity may allow for the more accurate detection of cancer cells, representing a clinically relevant method for the imaging of brain metastases.

The U.S. multicenter, open-label, single arm Phase 2b clinical trial is evaluating the diagnostic performance of 18F-RAD101 in 30 individuals with confirmed recurrent brain metastases from solid tumors of different origins. The primary objective of the study is concordance between 18F-RAD101 positive lesions and those seen in conventional imaging (MRI with gadolinium) in participants with suspected recurrent brain metastases. RAD 101 received U.S. Food and Drug Administration (FDA) Fast Track Designation to distinguish between recurrent disease and treatment effect of brain metastases originating from solid tumors of different origin, including leptomeningeal disease.

In the U.S. alone, there are more than 300,000 patients diagnosed annually with cerebral metastases. The incidence of Intracranial Metastatic Disease (IMD) continues to increase, in part, due to improvements in systemic therapy resulting in a more durable control of the primary tumor. Contrast-enhanced Magnetic Resonance Imaging (CE-MRI) is the preferred method for imaging IMD, but has limitations, particularly in follow-up surveillance scans to optimise patient care.^1^

^1^	A hybrid [18F]fluoropivalate PET-multiparametric<br>MRI to detect and characterise brain tumour metastases based on a permissive environment for monocarboxylate transport	European Journal<br>of Nuclear Medicine and Molecular Imaging

Radiopharm Theranostics LimitedSuite 1, Level 3, 62 Lygon Street, Carlton South VIC 3053 AustraliaABN: 57 647 877 889

ASX ANNOUNCEMENT<br><br> <br>16 APRIL 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, and brain metastases. Learn more at radiopharmtheranostics.com.

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

For more information:

Riccardo Canevari

CEO & Managing Director

P: +1 862 309 0293

E: [email protected]

Anne Marie Fields

Precision AQ (Formerly Stern IR)

E: [email protected]

Paul Hopper

Executive Chairman

P: +61 406 671 515

E: [email protected]

Media

Matt Wright

NWR Communications

P: +61 451 896 420

E: [email protected]

Follow Radiopharm Theranostics:

Website – https://radiopharmtheranostics.com/

Twitter – https://twitter.com/TeamRadiopharm

Linked In – https://www.linkedin.com/company/radiopharm-theranostics/

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

Radiopharm Theranostics LimitedSuite 1, Level 3, 62 Lygon Street, Carlton South VIC 3053 AustraliaABN: 57 647 877 889

RADX 6-K