Leak of Moderna-Merck cancer vaccine phase 3 data sparks drama at ESMO 2026 conference

The European Society for Medical Oncology (ESMO) meeting this year was marked by an unexpected leak of phase 3 results for a cancer vaccine being developed by Moderna and Merck. The data appeared two days before the scheduled Presidential Symposium, drawing immediate attention from attendees.

Merck's vice president of global clinical development, Shweta Jain, told Fierce that the premature disclosure was "unfortunate," but emphasized that the company and its partner would still present the trial findings as planned on Saturday.

Despite the early leak, the symposium still attracted large crowds, with many delegates filling the Alicante Auditorium and some standing outside due to limited seating. The atmosphere was described as slightly muted compared to the usual high‑energy anticipation for such data releases.

ESMO also introduced a new policy that barred journalists from entering the exhibition halls, aiming to control information flow after the leak.