Xeris details Phase 3 plan for weekly hypothyroidism therapy XP-8121

Xeris Biopharma Holdings, Inc. hosted an XP-8121 Program Overview webinar on September 9, 2026, according to an 8-K filing. The company held the webinar and furnished the slide presentation used by senior management in discussions with investors as an exhibit to the filing.¹

The presentation lays out a clinical development plan built around three studies. The Cornerstone Phase 3 study will enroll 500 participants at more than 50 U.S. sites, treating well-controlled adults and adolescents with hypothyroidism for 54 weeks, randomized 1:1 to daily oral levothyroxine or once-weekly subcutaneous XP-8121, with a 15% non-inferiority margin and a primary endpoint of the proportion of participants with TSH within normal range at both 48 and 54 weeks.¹ A separate Capstone study will evaluate dose conversion in pediatrics, following completed Phase 1 and Phase 2 studies in adults that established dose conversion, while a Touchstone study is expected to assess efficacy in patients with inconsistent or inadequate control.¹

On timing, Xeris said the Cornerstone trial is expected to initiate by year-end 2026, aligned with FDA feedback on endpoints and statistical power, with data expected in late 2028 and anticipated approval and launch in 2030.¹

The company cited a market opportunity based on its own analysis. Xeris said that of U.S. patients treated for hypothyroidism, about 20%, or 3 to 5 million patients, are failing on existing treatments.¹ The company put the potential peak net revenue for XP-8121 at $1 billion to $3 billion,¹ a figure disclosed at its June 2025 Analyst Day.¹

Xeris said it holds issued patents covering compositions of matter and methods of use for XP-8121, with intellectual property coverage through at least 2043.¹ The filing also noted the company issued a related press release the same day, furnished as Exhibit 99.2.