SEC Form 6-K filed by Radiopharm Theranostics Limited

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 March 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 March 27, 2026 titled:

“RAD Doses First Patient in RAD 402 Phase 1 Clinical Study”

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

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.

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