Company: NCNA
Filing Date: 2025-08-01
Form Type: 6-K
Source: 0001193125-25-171672
Chunk: 0

Company: NuCana plc
Filing Date: 2025-08-01
Form: 6-K
Chunk 0
---
### UNITED STATES

### SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

OF THE SECURITIES EXCHANGE ACT OF 1934

For the month of August 2025

(Commission File No. 001-38215)

### NUCANA PLC
(Translation of registrant’s name into English)

3 Lochside Way

Edinburgh EH12 9DT

United Kingdom

(Address of registrant’s principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under
cover 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): ☐

NuCana plc announces ADS ratio change On August 1, 2025, NuCana plc (the “Company”) announced that the Company will implement the Company’s previously disclosed plans to change the ratio of its American Depositary Shares (“ADSs”) to its ordinary shares from one (1) ADS, representing twenty-five (25) ordinary shares, to one (1) ADS, representing five thousand (5,000) ordinary shares (the “ADS Ratio”). For the Company’s ADS holders, the change in the ADS ratio has the same effect as a one-for-two-hundredreverse ADS split and has no impact on an ADS holder’s proportional equity interest in the Company. As previously disclosed, the ratio change was expected to become effective with respect to the ADS trading price on the Nasdaq Capital Market at the opening of trading on August 8, 2025. The effective date has been adjusted, and the ratio change will now take effect at the opening of trading on August 11, 2025. Further information is set out in the press release attached hereto as Exhibit 99.1 and which is incorporated by reference herein. The information contained in this Form 6-Kis hereby incorporated by reference into the Company’s Registration Statement on Form F-3,as amended (File No. 333-281576),