Form 8-K

8-K — Onconetix, Inc.

Accession: 0001213900-26-056109

Filed: 2026-05-14

Period: 2026-05-13

CIK: 0001782107

SIC: 2834 (PHARMACEUTICAL PREPARATIONS)

Item: Other Events

Item: Financial Statements and Exhibits

Documents

8-K — ea0290739-8k_onconetix.htm (Primary)

EX-99.1 — PRESS RELEASE, DATED MAY 13, 2026 (ea029073901ex99-1.htm)

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8-K — CURRENT REPORT

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of report (Date of earliest event reported):

May 13, 2026

Onconetix, Inc.

(Exact name of registrant as specified in its charter)

Delaware

001-41294

83-2262816

(State or other jurisdiction

of incorporation)

(Commission File Number)

(IRS Employer

Identification No.)

201 E. Fifth Street, Suite 1900

Cincinnati, Ohio

45202

(Address of principal executive offices)

(Zip Code)

Registrant’s telephone number, including

area code: (513) 620-4101

Not Applicable

(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:

☐ Written communications pursuant to Rule 425 under the Securities

Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange

Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b)

under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c)

under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b)

of the Act:

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common Stock, par value $0.00001 per share

ONCO

The Nasdaq Stock Market LLC

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. ☐

Item 8.01 Other Events.

May 13, 2026, Onconetix, Inc. issued a press release on the first quarter operational and clinical progress of its fully-owned Swiss subsidiary,

Proteomedix AG, a developer of Proclarix®, a diagnostic blood test used in combination with prostate-specific antigen to identify

clinically significant prostate cancer. The press release details, among other things, two recently published peer-reviewed papers on

the performance and prognostic value of Proclarix, as well as the initiation of a multi-center clinical study with Labcorp Holdings Inc.

in the U.S. to evaluate Proclarix.

copy of the press release is filed as Exhibit 99.1 to this Current Report on Form 8-K.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

The following exhibits are being filed or furnished,

as applicable, with this Current Report on Form 8-K:

Exhibit No.

Description

99.1

Press Release, dated May 13, 2026.

104

Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURES

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 hereunto duly authorized.

Onconetix, Inc.

May 13, 2026

By:

/s/ David Allan White

Name:

David Allan White

Title:

Chief Executive Officer

EX-99.1 — PRESS RELEASE, DATED MAY 13, 2026

EX-99.1

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Exhibit 99.1

Onconetix Reports Q1 2026 Progress at Proteomedix

AG, Including Two New Peer-Reviewed

Publications and Initiation of U.S. Validation Study

New Clinical Data Reinforce Proclarix®

Performance in Reducing Overdiagnosis and Unnecessary Biopsies; Multi-Center PRIME Study Initiated in Collaboration with Labcorp; European

Commercial Expansion Advances

CINCINNATI, Ohio, May 13, 2026 (GLOBE NEWSWIRE) — Onconetix,

Inc. (Nasdaq: ONCO) (“Onconetix” or the “Company”) today provided an update on the Q1 2026 operational progress

of its fully-owned Swiss subsidiary, Proteomedix AG (“PMX”), developer of Proclarix®, a CE-IVD certified diagnostic blood

test used in combination with PSA (prostate-specific antigen) to identify clinically significant prostate cancer (“csPCa”).

Prostate cancer is the most frequently diagnosed male cancer in most

countries globally and represents a significant burden to patients and healthcare systems. Proclarix® is designed to support clinicians

in distinguishing clinically significant from clinically insignificant prostate cancer at an early stage, reducing unnecessary biopsies

and overdiagnosis.

New Peer-Reviewed Clinical Publications

Two new peer-reviewed scientific publications from a recent clinical

study conducted in Denmark further reinforce the clinical utility of Proclarix®.

The first paper, by Schiess et al., has been accepted for publication

in BMC Cancer, a renowned open-access oncology research journal. The study evaluated Proclarix® in a cohort of 371 men and demonstrated

its superior performance in ruling out clinically insignificant or absent prostate cancer while maintaining a low risk of missing csPCa.

Proclarix® was shown to significantly reduce overdiagnosis and unnecessary biopsies, outperforming both %fPSA and the ERSPC risk calculator.

The second paper, by Athanasiou et al., has been published in the journal

Cancers (2026, 18, 1348-62). In a cohort of 132 men under active surveillance, the study demonstrated the prognostic value of Proclarix®

and its risk score in predicting the transition of patients from active surveillance to active treatment.

PRIME Study Initiated with Labcorp

To evaluate Proclarix® in the U.S. market and across various ethnicities,

PMX has initiated the PRIME study, a multi-center clinical validation study conducted in collaboration with Labcorp Holdings Inc. The

first participants have been enrolled, and the study is designed to ultimately include up to 500 men.

European Commercial Expansion

PMX continued to advance its commercial presence across Europe during

Q1 2026. In the United Kingdom, Proclarix® is now offered by a patient organization as an additional option within a real-world screening

initiative for early identification of prostate cancer. Close to 100 Proclarix® tests were carried out within this initiative in Q1

2026 alone.

PMX has also identified a collaboration partner in Turkey and continues

its efforts to expand market reach into additional European countries.

About Onconetix, Inc.

Onconetix, Inc. (Nasdaq: ONCO) is a commercial-stage biotechnology

company focused on the research, development, and commercialization of innovative oncology solutions. Onconetix owns Proclarix®, an

in vitro diagnostic test for prostate cancer originally developed by Proteomedix and approved for sale in the European Union under the

IVDR, which it anticipates will be marketed in the U.S. as a lab developed test through its license agreement with Labcorp. For more information,

visit www.onconetix.com.

About Proteomedix AG

Proteomedix AG (PMX) is a fully owned Swiss subsidiary of Onconetix,

Inc. focused on the development and commercialization of innovative diagnostic solutions for prostate cancer. PMX developed Proclarix®,

a CE-IVD certified diagnostic blood test that, when used in combination with PSA, supports the early identification of clinically significant

prostate cancer. PMX is headquartered in Switzerland. For more information, visit www.proteomedix.com.

Forward-Looking Statements

Certain statements in this press release are forward-looking within

the meaning of the Private Securities Litigation Reform Act of 1995. These statements may be identified by the use of forward-looking

words such as “anticipate,” “believe,” “forecast,” “estimate,” “expect,” and

“intend,” among others. These forward-looking statements are based on Onconetix’s current expectations and actual results

could differ materially. Investors should read the risk factors set forth in Onconetix’s Annual Report on Form 10-K filed with the

SEC on March 13, 2026, and periodic reports filed with the SEC on or after the date thereof. All forward-looking statements are expressly

qualified by all such risk factors and other cautionary statements. The information set forth herein speaks only as of the date hereof.

Onconetix does not undertake an obligation to update or revise any forward-looking statement except as required by applicable law.

Investor and Media Contact:

Onconetix, Inc.

201 E. Fifth Street, Suite 1900

Cincinnati, OH 45202

Phone: (513) 620-4101

Email: investors@onconetix.com

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