Day One Completes Acquisition of Mersana Therapeutics

Rhea-AI Summary

Day One (Nasdaq: DAWN) completed its acquisition of Mersana Therapeutics on January 6, 2026, acquiring all outstanding shares for $25 per share in cash plus one non-tradable contingent value right (CVR) per share for potential milestone payments up to $30.25 per CVR, for total consideration of up to $55.25 per share.

The tender offer expired Jan. 5, 2026 with 3,029,135 shares validly tendered (representing 60.57% of Mersana outstanding). Following a statutory merger under Delaware law, Mersana became a direct wholly owned subsidiary of Day One and its Nasdaq common stock will be delisted prior to market open on Jan. 6, 2026. Day One adds clinical-stage ADC emiltatug ledadotin (Emi-Le), targeting B7-H4 and adenoid cystic carcinoma (ACC), to its pipeline.

Positive

• Cash acquisition price of $25 per share
• Upside via CVR up to $30.25 per CVR (total up to $55.25 per share)
• Clinical-stage asset added: Emi-Le targeting ACC (B7-H4)
• Transaction closed and Mersana became a wholly owned subsidiary on Jan 6, 2026

Negative

• CVR non-tradable, limiting immediate liquidity for milestone upside
• Milestone payments conditional, creating uncertainty about full $30.25 CVR value
• Mersana common stock delisted from Nasdaq prior to market open on Jan 6, 2026

Key Figures

Cash offer price $25 per share Cash consideration for each Mersana common share

CVR potential Up to $30.25 per CVR Non-tradable CVR milestone payments per Mersana share

Total consideration Up to $55.25 per share Maximum cash value per Mersana share including CVR

Shares tendered 3,029,135 shares Mersana common stock validly tendered at offer expiration

Tender participation 60.57% of shares Portion of Mersana outstanding common stock tendered

CVR milestones Up to $30.25 per CVR Clinical, regulatory, and sales milestone-dependent cash payments

Market Reality Check

$8.64 Last Close

Volume Volume 1,589,316 is at 0.59x the 20-day average of 2,706,347, indicating subdued trading. low

Technical Shares at $8.55 are trading above the 200-day MA of $7.42, but remain 36.81% below the 52-week high.

Peers on Argus

DAWN fell 3.39% while several biotech peers also traded lower (e.g., AVBP -6.06%, KURA -6.93%, PRAX -3.89%), but no coordinated sector momentum was flagged by the scanner.

Historical Context

Date	Event	Sentiment	Move	Catalyst
Dec 16	Conference participation	Neutral	-0.2%	J.P. Morgan Healthcare Conference presentation announcement and webcast details.
Nov 24	Clinical data update	Positive	+4.2%	Three-year follow-up data from OJEMDA Phase 2 FIREFLY-1 trial in pLGG.
Nov 18	Conference participation	Neutral	-3.0%	Participation in Piper Sandler healthcare conference with fireside chat.
Nov 13	Acquisition announcement	Positive	-14.4%	Definitive agreement to acquire Mersana and add Emi‑Le ADC to pipeline.
Nov 10	Upcoming data	Positive	+4.4%	OJEMDA long-term data slated for oral presentation at SNO meeting.

Pattern Detected

Positive clinical and data updates have generally seen aligned price gains, while the prior Mersana acquisition announcement coincided with a sharp negative reaction.

Recent Company History

Over the past months, Day One has highlighted OJEMDA data and investor conference participation, alongside announcing and then progressing the Mersana acquisition. The initial acquisition agreement on Nov 13, 2025 added the Emi‑Le ADC and coincided with a -14.41% move, suggesting investor caution on deal economics. Subsequent OJEMDA data on Nov 24, 2025 and follow-up presentations supported the core pediatric oncology franchise, while today’s news confirms closing of the Mersana transaction first outlined in November.

Market Pulse Summary

This announcement confirms completion of Day One’s acquisition of Mersana, adding the Emi‑Le antibody-drug conjugate and making Mersana a wholly owned subsidiary via a 251(h) merger. Earlier news on Nov 13, 2025 outlined identical terms of up to $55.25 per share. Investors may track future updates on Emi‑Le’s clinical progress, integration milestones, and how this deal complements OJEMDA data already highlighted in recent regulatory filings.

Key Terms

antibody drug conjugate medical

"clinical-stage antibody drug conjugate (ADC) emiltatug ledadotin (Emi-Le)"

An antibody drug conjugate is a targeted medical treatment that combines a special antibody with a powerful drug, allowing precise delivery of the medicine directly to cancer cells or other harmful cells in the body. For investors, it represents a sophisticated approach to therapy that could improve treatment effectiveness and reduce side effects, potentially leading to significant growth opportunities in the biotech and pharmaceutical sectors.

ADC medical

"clinical-stage antibody drug conjugate (ADC) emiltatug ledadotin (Emi-Le)"

An antibody-drug conjugate (ADC) is a targeted cancer medicine that pairs an antibody that recognizes specific markers on tumor cells with a potent cell-killing drug, connected so the toxic payload is delivered directly to the cancer. For investors, ADCs matter because successful ADCs can improve patient outcomes and reduce side effects compared with traditional chemotherapy, shaping clinical trial success, regulatory approval chances, commercial demand, and a company’s valuation much like a guided missile versus a general bomb.

contingent value right financial

"plus one non-tradable contingent value right (“CVR”) per share"

A contingent value right is a special security that gives its holder the right to receive one or more future payments only if specified events happen, such as a product reaching a sales target or getting regulatory approval. It matters to investors because it offers potential extra payout tied to uncertain outcomes—like a bet that a project will succeed—so it can add upside to a deal while also carrying extra risk and valuation uncertainty.

CVR financial

"plus one non-tradable contingent value right (“CVR”) per share"

A CVR (Contingent Value Right) is a contract-like entitlement issued in corporate transactions that pays the holder additional cash or shares only if specified future events or milestones occur, such as regulatory approval, sales targets, or performance thresholds. Think of it like a coupon that becomes valuable only if a company hits agreed goals; for investors it changes the risk-reward mix of a deal by offering potential upside tied to uncertain future outcomes and can affect valuation, liquidity and expected returns.

tender offer financial

"completion of all conditions of the tender offer to acquire all outstanding shares"

A tender offer is a proposal made by a person or company to buy shares from existing shareholders at a set price, usually higher than the current market value, within a specific time frame. It matters to investors because it can lead to a change in ownership or control of a company, and shareholders must decide whether to sell their shares at the offered price.

Section 251(h) regulatory

"following a statutory merger under Section 251(h) of the Delaware General"

Section 251(h) is a provision in Delaware corporate law that lets a company complete a merger without holding a separate shareholder vote if a prior, qualifying tender offer already secured the required number of shares on the same terms. For investors, it matters because it shortens the timetable and reduces the risk that a merger will be blocked by a follow-up vote—think of it as a shortcut that finalizes a deal once enough stockholders have already agreed.

Delaware General Corporation Law regulatory

"under Section 251(h) of the Delaware General Corporation Law on January 6"

A set of state laws that acts like a rulebook for how corporations are formed, governed, and dissolved in Delaware. It lays out legal duties for company leaders, protections and voting rights for shareholders, and rules for mergers and other big transactions, giving investors clearer expectations about how corporate decisions are made and disputes are resolved—similar to having standardized traffic laws for business behavior.

AI-generated analysis. Not financial advice.

Acquisition expands Day One’s pipeline with clinical-stage antibody drug conjugate (ADC) emiltatug ledadotin (Emi-Le) targeting rare cancer adenoid cystic carcinoma (ACC)

BRISBANE, Calif., Jan. 06, 2026 (GLOBE NEWSWIRE) -- Day One Biopharmaceuticals, Inc. (Nasdaq: DAWN) (“Day One”), a biopharmaceutical company dedicated to developing and commercializing targeted therapies for people of all ages with life-threatening diseases, today announced the successful close of its acquisition of Mersana Therapeutics, Inc., (NASDAQ: MRSN) (“Mersana”) following completion of all conditions of the tender offer to acquire all outstanding shares of Mersana at a price of $25 per share in cash, plus one non-tradable contingent value right (“CVR”) per share to receive certain potential milestone payments of up to an aggregate of $30.25 per CVR in cash.

“This acquisition of Mersana is a strategic fit with Day One’s mission and ambitions, allowing us to continue to expand into adult oncology while maintaining a focus on rare cancers. With promising early clinical data, Emi-Le represents a potentially transformative advancement in the treatment of ACC, and we will leverage our distinct capabilities to rapidly develop the asset and pursue registration to reach patient communities who have no approved therapies today,” said Jeremy Bender, Ph.D., chief executive officer of Day One. “Building on the strong momentum of OJEMDA in the market and our continually progressing pipeline, this acquisition strengthens our overall position to expand our impact on patient communities while delivering sustainable business growth.”

Through this acquisition, Day One has added a second novel ADC to the company’s clinical pipeline. Emi-Le (emiltatug ledadotin) represents an innovative and differentiated ADC directed against B7-H4, a well-characterized target in certain cancers including adenoid cystic carcinoma (ACC), a challenging rare cancer usually arising within the salivary gland with a clear unmet medical need. For additional background on Emi-Le and the acquisition, please read the announcement press release and view Day One’s investor presentation.

Terms of the Acquisition
Day One has acquired all outstanding shares of Mersana common stock at a price of $25 per share in cash, plus one non-tradable CVR per share to receive certain potential milestone payments of up to an aggregate of $30.25 per CVR in cash, for total consideration of up to $55.25 per share in cash. The CVR is payable subject to certain terms and conditions of achievement of specified milestones.

The tender offer expired as scheduled at one minute following 11:59 p.m., Eastern Time, on January 5, 2026 (the “Expiration Date”). The depositary for the tender offer, Computershare Trust Company, N.A., advised Day One that, as of the Expiration Date, a total of 3,029,135 shares of Mersana common stock were validly tendered and not validly withdrawn pursuant to the tender offer, representing 60.57% of the outstanding shares of Mersana common stock and satisfying the minimum condition to consummate the tender offer. All of the conditions of the tender offer having been satisfied, Day One accepted for payment all such tendered shares, and following a statutory merger under Section 251(h) of the Delaware General Corporation Law on January 6, 2026, Mersana became a direct wholly owned subsidiary of Day One. All remaining shares of Mersana common stock that were not tendered in the tender offer were converted into the right to receive the same per share consideration as shares that were tendered in the tender offer, as described above. With the completion of the acquisition, Mersana’s common stock will cease to trade on the Nasdaq stock exchange prior to market open on January 6, 2026 and Mersana’s common stock will be delisted from Nasdaq.

Advisors
Gordon Dyal & Co., LLC acted as the exclusive financial advisor to Day One, with Fenwick & West LLP serving as legal counsel. TD Cowen acted as financial advisor to Mersana, with Wilmer Cutler Pickering Hale and Dorr LLP serving as legal counsel.

About Day One Biopharmaceuticals
Day One Biopharmaceuticals is a commercial-stage biopharmaceutical company that believes when it comes to pediatric cancer, we can do better. The Company was founded to address a critical unmet need: the dire lack of therapeutic development in pediatric cancer. Inspired by “The Day One Talk” that physicians have with patients and their families about an initial cancer diagnosis and treatment plan, Day One aims to re-envision cancer drug development and redefine what’s possible for all people living with cancer—regardless of age—starting from Day One.

Day One partners with leading clinical oncologists, families, and scientists to identify, acquire, and develop important targeted cancer treatments. Day One’s pipeline includes tovorafenib (OJEMDA™), DAY301, and following the January 2026 acquisition of Mersana Therapeutics, Emi-Le (emiltatug ledadotin), a novel antibody drug conjugate (ADC) targeting the B7-H4 protein in clinical development to treat the rare cancer adenoid cystic carcinoma (ACC).

Day One is based in Brisbane, California. For more information, please visit www.dayonebio.com or find Day One on LinkedIn or X.

Day One uses its Investor Relations website (ir.dayonebio.com), its X handle (x.com/DayOneBio), and LinkedIn Home Page (linkedin.com/company/dayonebio) as a means of disseminating or providing notification of, among other things, news or announcements regarding its business or financial performance, investor events, press releases, and earnings releases, and as a means of disclosing material nonpublic information and for complying with its disclosure obligations under Regulation FD.

Cautionary Note Regarding Forward-Looking Statements
This press release contains “forward-looking” statements, including, but not limited to: Day One’s plans to develop and commercialize cancer therapies and its pipeline, including the ability of Emi-Le to treat ACC or other cancers, statements regarding the payment and timing of payment of the offer to former Mersana common stockholders, the ability and timing of delisting of Mersana common stock, and the ability to achieve any milestones under the CVR within the milestone payment period under the CVR. Statements including words such as “believe,” “plan,” “continue,” “expect,” “will,” “develop,” “signal,” “potential,” or “ongoing” and statements in the future tense are forward-looking statements. These forward-looking statements involve risks and uncertainties, as well as assumptions, which, if they do not fully materialize or prove incorrect, could cause our results to differ materially from those expressed or implied by such forward-looking statements.

Forward-looking statements are subject to risks and uncertainties that may cause Day One’s actual activities or results to differ significantly from those expressed in any forward-looking statement, including risks and uncertainties in this press release and other risks set forth in our filings with the Securities and Exchange Commission, including risks related to the ability to realize the anticipated benefits of the acquisition, including the possibility that the expected benefits from the acquisition will not be realized or will not be realized within the expected time period; the risk that the businesses will not be integrated successfully; disruption from the transaction making it more difficult to maintain business and operational relationships; negative effects of the consummation of the acquisition on the market price of Day One’s common stock and/or operating results; significant transaction costs; unknown liabilities; Day One’s ability to develop, obtain and retain regulatory approval for or commercialize any product candidate; Day One’s ability to protect intellectual property; the potential impact of global business or macroeconomic conditions, including as a result of inflation, rising interest rates, instability in the global banking system, geopolitical conflicts and the sufficiency of Day One’s cash, cash equivalents and investments to fund its operations. These forward-looking statements speak only as of the date hereof and Day One specifically disclaims any obligation to update these forward-looking statements or reasons why actual results might differ, whether as a result of new information, future events or otherwise, except as required by law.

DAY ONE MEDIA
media@dayonebio.com

DAY ONE INVESTORS
LifeSci Advisors, PJ Kelleher
pkelleher@lifesciadvisors.com

FAQ

What did Day One (DAWN) pay to acquire Mersana and when did the deal close?

Day One paid $25 per share in cash plus one non-tradable CVR per share; the merger closed on January 6, 2026.

What is the contingent value right (CVR) in the DAWN acquisition of Mersana?

Each acquired share includes one non-tradable CVR that may pay up to an aggregate of $30.25 in cash, subject to specified milestone conditions.

How many Mersana shares were tendered in the Day One offer and what percentage did that represent?

3,029,135 shares were validly tendered, representing 60.57% of outstanding Mersana common stock as of the offer expiration.

What pipeline asset did Day One acquire from Mersana (DAWN)?

Day One added emiltatug ledadotin (Emi-Le), a clinical-stage antibody drug conjugate directed at B7-H4 for adenoid cystic carcinoma (ACC).

Will Mersana stock continue trading after the DAWN acquisition?

No; Mersana common stock will be delisted from Nasdaq and will cease trading prior to market open on January 6, 2026.