Company: NCNA
Filing Date: 2025-06-27
Form Type: 6-K
Source: 0001193125-25-151430
Chunk: 2

Company: NuCana plc
Filing Date: 2025-06-27
Form: 6-K
Chunk 2
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 description of the Jefferies Sales Agreement is not complete and is qualified in its entirety by reference to the full text of the Jefferies Sales Agreement, a copy of which was filed as Exhibit 1.2 to our Registration Statement on Form F-3,filed with the U.S. Securities and Exchange Commission on August 19, 2021. The information in this Form 6-Kshall be deemed to be incorporated by reference into the registration statements on Form F-3,as amended (File Number 333-281576)and Form S-8(File Number 333-223476and File Number 333-248135),and related prospectuses, as such registration statements and prospectuses may be amended from time to time, and to be a part thereof from the date on which this report is filed, to the extent not superseded by documents or reports subsequently filed or furnished. Exhibits

| Exhibit |     | Description              |
| 10.1    |     | Form of Letter Agreement |

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: June 27, 2025