Company: NCNA
Filing Date: 2025-07-21
Form Type: 6-K
Source: 0001193125-25-161557
Chunk: 0

Company: NuCana plc
Filing Date: 2025-07-21
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 July 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 warrant cancellation On July 21, 2025, NuCana plc announced the cancellation of all outstanding Series A ADS Purchase Warrants following a strategic ATM execution. Further information is included in the press release attached as Exhibit 99.1 hereto, which is incorporated by reference herein. Exhibits

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, thereto duly authorized.

| NuCana plc |     |                                 |
| By:        |     | /s/ Ian Webster                 |
| Name:      |     | Ian Webster                     |
| Title:     |     | Interim Chief Financial Officer |

Date: July 21, 2025