EX-32.1 4 lptx-20250630xex32d1.htm EX-32.1

Exhibit 32.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER

AND CHIEF FINANCIAL OFFICER

PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Quarterly Report of Leap Therapeutics, Inc. (the “Company”) on Form 10-Q for the quarter ended June 30, 2025, as filed with the Securities and Exchange Commission on the date hereof (the “Report”), I, Douglas E. Onsi, as Chief Executive Officer, President and Chief Financial Officer, hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to my knowledge:

(1) | The Report fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

(2) | The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

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Date: August 13, 2025 | By: | /s/ DOUGLAS E. ONSI
​ | ​ | Douglas E. Onsi
​ | ​ | President, Chief Executive Officer and Chief Financial Officer
​ | ​ | (Principal Executive Officer and Principal Financial Officer)

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This certification accompanies the Form 10-Q to which it relates, is not deemed filed with the Securities and Exchange Commission and is not to be incorporated by reference into any filing of Leap Therapeutics, Inc. under the Securities Act of 1933, as amended, or the Securities Exchange Act of 1934, as amended (whether made before or after the date of the Quarterly Report), irrespective of any general incorporation language contained in such filing.