AstraZeneca Makes $2 Billion Strategic Equity Investment in Summit Therapeutics (Form 8-K)

AstraZeneca Makes $2 Billion Strategic Equity Investment in Summit Therapeutics

Investment in Preferred Shares Convertible to Common Equity, Equivalent to a Per-Share Price of Summit's Common Stock of $18.36, Representing a Premium over Today's Closing Trading Price

Summit Also Enters into Clinical Trial Collaboration with AstraZeneca to Evaluate Ivonescimab in Combination with Sonesitatug Vedotin in Multiple Gastrointestinal Cancers

Summit & AstraZeneca Plan to Enter into a Clinical Trial Collaboration Combining Ivonescimab with Multiple AstraZeneca ADCs and Other Cancer Medicines

Miami, Florida, September 28, 2026 - Summit Therapeutics Inc. (Nasdaq: SMMT) today announced key developments important to the company's progress towards achieving its goal of making a significant difference in the lives of patients with cancer. Specifically, Summit has established agreements with AstraZeneca (LSE/STO/NYSE: AZN) for a strategic equity investment in Summit and a clinical collaboration focused on ivonescimab and sonesitatug vedotin (sone-ve). Moreover, Summit and AstraZeneca intend to evaluate ivonescimab with an additional set of AstraZeneca's cancer medicines, including other antibody drug conjugates (ADCs). Ivonescimab is a novel, potential first-in-class investigational PD-1 / VEGF bispecific antibody.

AstraZeneca Equity Investment in Summit

Summit and AstraZeneca have entered into an agreement whereby AstraZeneca will make an equity investment of $2.0 billion in convertible preferred shares. At the conversion ratio, the investment represents a common stock price equal to $18.36, representing a premium over today's closing price.

"This significant investment, as well as the collaboration, is a powerful validation of the potential of ivonescimab," said Robert W. Duggan, Chairman and Co-Chief Executive Officer of Summit Therapeutics. "We are proud to welcome AstraZeneca as a strategic investor as we continue to work with purposeful urgency to make a significant difference for patients with cancer by improving outcomes."

Summit - AstraZeneca Clinical Trial Collaboration: Ivonescimab and Sone-Ve

Summit entered into a clinical collaboration agreement with AstraZeneca to evaluate sonesitatug vedotin in combination with ivonescimab with the intent to start studies in certain gastrointestinal (GI) cancer settings imminently. Sone-ve is a potential global first-in-class Claudin 18.2-targeting ADC with several ongoing trials underway in GI cancers.

Under the terms of the clinical collaboration agreement, each company will contribute their respective compound for the combination studies to be conducted, and the parties will jointly contribute to the costs of such studies, which are intended to be sponsored by AstraZeneca. Each company will retain development and commercial rights to their respective molecules.

"The developments announced today with AstraZeneca open an exciting new chapter in the advancement of ivonescimab," said Dr. Maky Zanganeh, President and Co-Chief Executive Officer of Summit Therapeutics. "With a growing body of evidence supporting ivonescimab's differentiated PD-1 / VEGF bispecific approach, we look

forward to further broadening the development plan of ivonescimab and initiating new clinical trials exploring the potential to combine ivonescimab with promising novel anti-cancer compounds, including ADCs, to bring together complementary approaches to tumor-cell killing, antitumor immunity, and the tumor microenvironment."

AstraZeneca recently reported positive high-level results from the CLARITY-Gastric01 trial for sone-ve in 2nd and later-line Claudin18.2-positive advanced gastric cancers demonstrating a statistically significant and clinically meaningful improvement in overall survival (OS) versus investigator's choice of therapy. Results from this trial will be presented at the European Society for Medical Oncology Congress 2026 in a Presidential Symposium alongside the HARMONi-GI1 trial, an Akeso-sponsored trial from China in which ivonescimab plus chemotherapy demonstrated a statistically significant and clinically meaningful improvement in OS vs. durvalumab plus chemotherapy in first-line advanced biliary tract cancer.

Planned Summit - AstraZeneca Clinical Trial Collaboration: Ivonescimab and AZ's Cancer Medicines

Finally, Summit and AstraZeneca have executed a non-binding Memorandum of Understanding whereby the two companies intend to enter into an agreement to conduct clinical trials combining ivonescimab with multiple AstraZeneca's cancer medicines, including its leading portfolio of ADCs. The companies intend to share clinical development costs of potential future studies. Each company will retain their current development and commercial rights to their respective molecules, and the agreement is mutually non-exclusive. There are no additional financial considerations associated with milestones, royalties, revenue-sharing, or profit-sharing.

"A core pillar of our oncology strategy is to broaden the reach of our ADC portfolio as the backbone of treatment across tumor types with combinations alongside next-generation immunotherapies," said Susan Galbraith, Executive Vice President, Oncology Haematology R&D, AstraZeneca. "Bispecifics targeting PD-1 and VEGF are rapidly advancing in development and have the potential to improve on current immunotherapies, particularly in lung, breast and gastrointestinal cancers. This opportunity to combine ivonescimab with AstraZeneca's ADC portfolio, including with sone-ve, could enable new regimens that raise the bar for patients with cancer across the treatment landscape."

The Memorandum of Understanding with respect to the potential clinical trial collaboration between Summit and AstraZeneca is non-binding, and there can be no assurances that the intended clinical trial collaboration comes to fruition.

Financial Terms of AstraZeneca Equity Investment

Under the terms of the Share Purchase Agreement entered into by Summit and AstraZeneca, AstraZeneca will purchase an aggregate of approximately 108,955 shares of preferred stock convertible into shares of common stock of Summit at a 1:1,000 ratio. The total investment by AstraZeneca will be $2.0 billion. At the conversion ratio, the investment represents a common stock price equal to $18.36, the volume weighted-average price (VWAP) for the five trading days from the prior week plus 10%. Closing of the transaction is subject to customary conditions and is expected to occur by the end of this week.

The securities described above have not been registered under the Securities Act of 1933, as amended. Accordingly, these securities may not be offered or sold in the United States, except pursuant to an effective registration statement or an applicable exemption from the registration requirements of the Securities Act. Summit has agreed to file a registration statement with the Securities and Exchange Commission (SEC) registering the resale of the shares of common stock following the closing of the securities purchase agreement.