8-K/A

UNITED STATES

SECURITIES AND EXCHANGECOMMISSION

Washington, D.C. 20549

FORM 8-K/A

(Amendment No. 3)

CURRENT REPORT

Pursuant to Section13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Dateof earliest event reported): December 15, 2023

Onconetix, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code:

(513) 620-4101

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Explanatory Note

On December 21, 2023, Onconetix, Inc. (the “Company”) filed a Current Report on Form 8-K (the “Original Form 8-K”) with the Securities and Exchange Commission in connection with the Company’s acquisition of Proteomedix AG (“Proteomedix”), which Original Form 8-K was amended on December 27, 2023 and February 27, 2024 to, among other things, include the historical audited and interim financial statements of Proteomedix required by Item 9.01(a) of Form 8-K (the “Proteomedix Financial Statements”) and the pro forma combined financial information required by Item 9.01(b) of Form 8-K that were not included in the Original Form 8-K (together with the Proteomedix Financial Statements, the “Proteomedix Financial Information”) in reliance on the instructions to such item. This Amendment No. 3 on Form 8-K/A further amends the Original Form 8-K to add as an exhibit required by Item 9.01(d) a consent from BDO AG, Proteomedix’s independent registered public accounting firm (“BDO”) to incorporate by reference BDO’s audit report included in the Proteomedix Financial Information into certain of the Company’s registration statements. Except as described above, all other information in the Original Form 8-K remains unchanged.

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Item 9.01 FinancialStatements and Exhibits.

(d) Exhibits

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SIGNATURE

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

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Exhibit 23.1

Consent of Independent Registered Public Accounting Firm

We hereby consent to the incorporation by reference in Onconetix, Inc.’s (i) Registration Statements on Form S-8 (Nos. 333-268357, 333-265843 and  333-276824), (ii) Registration Statement on Form S-3 (No. 333-270383, 333-267142 and 333-264646) and (iii) Registration Statements on Form S-1(333-264646,  333-267142 and 333-277066), of our report dated February 14, 2024, relating to the financial statements of Proteomedix AG appearing in the Onconetix Inc. Proxy Statement for the year ended December 31, 2022 and 2021. Our report contains an explanatory paragraph regarding the Proteomedix AG’s ability to continue as a going concern.

BDO AG

Zurich, Switzerland

March 12, 2024

BDO Ltd, a limited company under Swiss law, incorporated in Zurich, forms part of the international BDO Network of independent member firms.