Summit Therapeutics Inc. (NASDAQ: SMMT) co-chief executive officer Robert Duggan acquired 3.81 million shares of common stock on June 12, 2026, at $13.12 per share, according to a Securities and Exchange Commission filing.

Following the transaction, Duggan directly owns 573.88 million shares of Summit Therapeutics. The purchase was coded as "P" in the filing, indicating a private purchase.

The filing also disclosed Duggan's indirect holdings through family trusts and relationships. These include 25.82 million shares held by the Mahkam Zanganeh Revocable Trust, with Duggan's spouse serving as trustee, and 10.2 million shares in the Shaun Zanganeh Irrevocable Trust, also with his spouse as trustee.

Additional indirect holdings include 76,680 shares owned by an immediate family member of his spouse and 31,000 shares held directly by his spouse.

Duggan serves as co-chief executive officer and director of Summit Therapeutics and is classified as a 10% owner of the company. The filing indicates he disclaims beneficial ownership of the indirectly held securities except to the extent of any pecuniary interest.