Summit Therapeutics Ivonescimab Phase 3 Bladder Cancer Trial Started September 10, 2026: HARMONi-GU1 With Enfortumab Vedotin

Summit Therapeutics' (SMMT) HARMONi-GU1 study — a randomized Phase 2/3 trial of ivonescimab in combination with enfortumab vedotin versus pembrolizumab in combination with enfortumab vedotin in previously untreated locally advanced or metastatic urothelial carcinoma — reached its registered start date of September 10, 2026, and our tracked record confirms the trial started on that exact date. For a company whose market capitalization stands at roughly $14.7 billion in our snapshot, and whose lead drug now has an FDA action date on the calendar in under two months, this recap covers what the start confirms, what the data shows around the program, and what remains unknown.

What happened

The tracked event record states:

• Event type: Phase 3 trial start (registered as a Phase 2/3 study).
• Expected start: September 10, 2026, "exact" date confidence.
• Outcome: started.
• Actual start: September 10, 2026 — the registration date was met exactly.
• Drug: ivonescimab (parsed from the registered title; our system resolves a canonical drug page for it).
• Known at: September 15, 2026 — the start confirmation entered our dataset five days after the event.

The registered design, in full: "A Randomized Phase 2/3 Study of Ivonescimab in Combination With Enfortumab Vedotin vs Pembrolizumab in Combination With Enfortumab Vedotin in Previously Untreated Locally Advanced or Metastatic Urothelial Carcinoma (HARMONi-GU1)."

What's verified

• Company: Summit Therapeutics Inc., ticker SMMT, active listing status, market capitalization $14,694,548,480 in our snapshot.
• Start confirmed: outcome field records "started" with actual date matching the expected date.
• Design elements: randomized; Phase 2/3; ivonescimab + enfortumab vedotin versus pembrolizumab + enfortumab vedotin; first-line (previously untreated) locally advanced or metastatic urothelial carcinoma; study name HARMONi-GU1.
• Ivonescimab trial footprint (from our drug-database linkage, which resolved for this article): 35 tracked trials with ivonescimab involvement — 23 Phase 2, 4 Phase 3, 1 Phase 2/3, 4 Phase 1/2, and 3 Phase 1 — with 25 recruiting, 8 not yet recruiting, and 2 active-not-recruiting. Earliest registered start June 27, 2022; latest registered start February 7, 2027.
• Institutional ownership (13F): 89 institutions holding $722,489,719 in filed positions as of quarter-end March 31, 2026. The five largest: BlackRock (9,653,758 shares, $183,035,250), State Street Corp (7,028,160 shares, $133,253,914), Vanguard Capital Management (5,711,802 shares, $108,295,766), UBS Group AG (3,680,315 shares, $69,778,773), and Geode Capital Management (3,315,854 shares, $62,886,714). Our data shows 12 quarterly trend points.

What remains unknown

• Enrollment size for HARMONi-GU1: UNKNOWN in our data.
• Primary endpoints: not specified in our structured fields beyond the registered framing.
• Results: any efficacy or safety outcome for this study is years of follow-up away and absent from our data.

The HARMONi pattern — and the PDUFA date behind it

HARMONi-GU1 is the third confirmed-start ivonescimab Phase 3 on our tracker, and the design logic repeats across all of them: put ivonescimab (or its combination) head-to-head against pembrolizumab-based control.

• HARMONi lung: a randomized, double-blinded, multiregional Phase 3 of ivonescimab versus pembrolizumab in first-line metastatic NSCLC with high PD-L1 expression — started February 27, 2025 (confirmed).
• Colorectal: a randomized, active-controlled, double-blind Phase 3 of ivonescimab + FOLFOX versus bevacizumab + FOLFOX in first-line metastatic colorectal cancer — started November 18, 2025 (confirmed).
• HARMONi-GU1 (this event): ivonescimab + enfortumab vedotin versus pembrolizumab + enfortumab vedotin in first-line urothelial carcinoma — started September 10, 2026 (confirmed).

And the near-term anchor: our calendar holds a PDUFA record for ivonescimab dated November 14, 2026 — an FDA target action date eight weeks out, with no outcome recorded yet. Three confirmed Phase 3 starts across three tumor types in nineteen months, a 35-trial footprint, and a pending FDA action date together frame HARMONi-GU1 not as an isolated event but as the newest node in the most aggressive head-to-head program we track.

One design detail in the registration deserves its own line: in HARMONi-GU1 both arms receive enfortumab vedotin — the experimental arm pairs it with ivonescimab, the control arm with pembrolizumab. The comparator architecture is therefore the same antibody-drug conjugate backbone in both arms, differing in the immune-system component on top of it. That is a fact of the registered title, not an inference about results; what it means for interpretability of the eventual readout is a question the trial itself will answer, and our data holds no outcome information for any of the three studies.

How to track it

• Summit Therapeutics company page: https://biosniper.co/company/SMMT
• HARMONi-GU1 event page: https://biosniper.co/calendar/event/5925590
• Ivonescimab drug page (35-trial footprint): https://biosniper.co/drug/ivonescimab

Bottom line

HARMONi-GU1 started on its exact registered date, September 10, 2026, putting ivonescimab plus enfortumab vedotin against pembrolizumab plus enfortumab vedotin in first-line advanced urothelial carcinoma. It is the third confirmed ivonescimab Phase 3 start in our tracker, inside a 35-trial program footprint, backed by 89 institutions holding $722 million in filed 13F positions — and it lands eight weeks before a November 14, 2026 PDUFA date for the same drug. Enrollment size and results are unknowns; the start itself, the design, and the calendar around it are the verified record.