Company: DAWN
Filing Date: 2025-11-14
Form Type: SC TO-C
Source: 0001104659-25-112478
Chunk: 0

Company: Day One Biopharmaceuticals, Inc.
Filing Date: 2025-11-14
Form: SC TO-C
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE TO

Tender Offer Statement under Section 14(d)(1) or 13(e)(1)

of the Securities Exchange Act of 1934

Mersana Therapeutics, Inc.

(Name of Subject Company (issuer))

Emerald Merger Sub, Inc.

(Offeror)

a wholly-owned subsidiary of

Day One Biopharmaceuticals, Inc.

(Parent of Offeror)

(Names of Filing Persons (identifying status as offeror, issuer or other person))

Common stock, $0.0001 par value per share

(Title of Class of Securities)

59045L106

(CUSIP Number of Class of Securities)

Jeremy Bender

Chief Executive Officer and President

Day One Biopharmaceuticals, Inc.

1800 Sierra Point Parkway, Suite 200

Brisbane, CA 94005

Telephone: (650)-484-0899

(Name, address, and telephone numbers of person authorized to receive notices and communications on behalf of filing persons)

Copy to:

Effie Toshav

Robert A. Freedman

Julia Forbess
Fenwick & West LLP
555 California Street
San Francisco, CA 94104
(415)-875-2300

CALCULATION OF FILING FEE</div>

| Transaction Valuation* |     | Amount of Filing Fee* |
| N/A                    |     | N/A                   |

* A
filing fee is not required in connection with this filing as it relates solely to preliminary communications made before the commencement
of the tender offer.

| x | Check the box if the filing relates solely to preliminary communications made before the commencement of a tender offer. |

Check the appropriate boxes below to designate any transactions to
which the statement relates:

| x | Third-party tender offer subject to Rule 14d-1. |

| ¨ | Going-private transaction subject to Rule 13e-3. |

| ¨ | Issuer tender offer subject to Rule 13e-4. |

| ¨ | Amendment to Schedule 13D under Rule 13d-2. |

Check the following box if the filing is a final amendment reporting
the results of the tender offer: ☐

If applicable, check the appropriate box(es) below to designate the
appropriate rule provision(s) relied upon:

| ¨ | Rule 13e-