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 OF THE

SECURITIES EXCHANGE ACT OF 1934

For the month of June 2018

Commission File Number: 001-32001

Aptose Biosciences Inc.

(Translation of registrant’s name into English)

251 Consumers Road, Suite 1105

Toronto, Ontario M2J 4R3

Canada

(Address of principal executive offices)

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 if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1)  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7)  ☐

INCORPORATION BY REFERENCE

This Report on Form 6-K is hereby incorporated by reference (i) as an Exhibit to the Registration Statement on Form F-10 of Aptose Biosciences Inc. (File No. 333-222909) and (ii) into the registration statement on Form F-3 of Aptose Biosciences Inc. (File No. 333-221783) and the prospectus included therein.

DOCUMENTS FILED AS PART OF THIS FORM 6-K

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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, thereunto duly authorized.

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