The extension will run until November 2019 with an option to add another year.
Summit will retain the exclusive rights to any intellectual property resulting from the alliance. The company will sponsor a drug discovery and development program at the university.
Under the extension, the company will increase the funding to £0.83m a year starting this month.
Isis Innovation, the research and technology commercialization company of the University of Oxford, continues to hold warrants over 354,090 ordinary shares that were granted under the original agreement signed in 2013.
The company may exercise all the warrants by February 2020, subject to achieving research, development and regulatory milestones.
Summit Therapeutics CEO Glyn Edwards said: "Summit’s strategic alliance with the University of Oxford is an important part of our DMD programme that seeks to discover and develop a strong pipeline of utrophin-based therapies for the treatment of all patients with DMD behind our lead clinical candidate SMT C1100.
"The extension of our alliance will allow us to invest further in utrophin modulation in partnership with the world-leading academic research groups at Oxford."
The collaboration has so far identified several utrophin modulator compounds that are structurally different from Summit’s SMT C1100 clinical candidate.
The US Food and Drug Administration and the European Medicines Agency granted orphan drug status to SMT C1100.