Lifestyle & Healthresearch summary
Moderna melanoma vaccine data leaks before ESMO in Madrid, and shares fall nearly 20%
Late-stage results for Moderna and Merck's personalized melanoma vaccine appeared online two days early, and the market reacted at once.
This article is general information, not medical advice. Talk to a doctor or another qualified professional about your own situation.
The leak
Moderna shares lost nearly 20% on Thursday, making the company a leading decliner in the S&P 500, after the most anticipated data at this year's ESMO conference in Madrid leaked before the meeting began [1][2]. Anyone following Moderna's push into cancer treatment, or the melanoma patients such a vaccine is meant for, has a stake in the results [3].
The leak was described as a major embargo violation of the most highly anticipated data presentation at ESMO, occurring on the eve of the conference [1]. STAT's reporters state they were not the source of the embargo violation [1].
What appeared online
Data from a late-stage trial of Moderna's mRNA-based melanoma vaccine, developed with Merck and called Intismeran, briefly appeared on the OncologyCentral website [2]. The results were originally scheduled for release on Saturday [2]. The companies had planned to present more details at the ESMO Congress 2026 on Saturday, but the leak preceded that presentation [2].
The leaked report said the vaccine combined with Keytruda lowered the risk of melanoma returning or death compared with immunotherapy alone [3]. Moderna declined to comment [3].
About the vaccine
Intismeran autogene is a personalized vaccine that Moderna and Merck developed together, which pairs the shot with Merck's Keytruda [3]. In August, Moderna and Merck said the trial met its main goals without releasing detailed results [3].
Moderna shares more than doubled in August after the companies reported those positive early results from the trial [2]. Moderna has described the melanoma readout as an important catalyst in its push to build an oncology franchise beyond respiratory vaccines [3].
How analysts and markets read it
Merck shares slipped 2% on Thursday [2]. Jefferies analysts called the data encouraging in a note to clients [2].
UBS analysts suggested the market's reaction could reflect outsized investor expectations, and said the results raised their confidence in related studies [2].
What it means for you
If you or someone you know is following this vaccine, the leaked report said the shot combined with Keytruda lowered the risk of melanoma returning or death compared with immunotherapy alone [3]. The detailed presentation was planned for Saturday at the ESMO Congress 2026, and the companies had intended to give more details there [2].
If you hold Moderna or Merck shares, Moderna fell nearly 20% on Thursday and Merck slipped 2% [2].
Sources
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