Company: DAWN
Filing Date: 2025-12-05
Form Type: SC TO-T
Source: 0001104659-25-118858
Chunk: 2

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-12-05
Form: SC TO-T
Chunk 2
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 November 13, 2025).                                                                                                                           | ​ |
| ​ | -d)(3       | ​ | ​ | Form of Contingent Value Rights Agreement (incorporated by reference to Exhibit 2.3 to the Current Report on Form 8-K (File No. 001-38129) filed by Mersana Therapeutics, Inc. with the Securities and Exchange Commission on November 13, 2025).                                                                                                                      | ​ |
| ​ | (d)(4)*     | ​ | ​ | Confidentiality Agreement, dated March 12, 2025, between Day One Biopharmaceuticals, Inc. and Mersana Therapeutics, Inc.                                                                                                                                                                                                                                               | ​ |
| ​ | -g          | ​ | ​ | Not applicable.                                                                                                                                                                                                                                                                                                                                                        | ​ |
| ​ | -h          | ​ | ​ | Not applicable.                                                                                                                                                                                                                                                                                                                                                        | ​ |
| ​ | 107*        | ​ | ​ | Filing Fee Table.                                                                                                                                                                                                                                                                                                                                                      | ​ |

* Filed herewith.

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### SIGNATURES
After due inquiry and to the best knowledge and belief of the undersigned, each of the undersigned certifies that the information set forth in this statement is true, complete and correct.

Date: December 5, 2025

#### EMERALD MERGER SUB, INC.
/s/ Charles N. York II

Name: Charles N. York II, M.B.A. 
 Title: Chief Executive Officer and President

#### DAY ONE BIOPHARMACEUTICALS, INC.
/s/ Jeremy Bender

Name: Jeremy Bender, Ph.D., M.B.A. 
 Title: Chief Executive Officer and President

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