Moderna shares plunge after leak of partial cancer vaccine data despite positive results

Moderna shares fell as much as 25% on Thursday after partial data on its cancer vaccine, developed with Merck, leaked before the full results were released. The stock declined despite the complete data, published later Thursday, meeting Wall Street expectations for the personalized treatment known as intismeran autogene.

The trial data showed that combining intismeran autogene with Merck's Keytruda lowered the likelihood of cancer returning or patients dying by 42% in certain melanoma cases, relative to using the immunotherapy alone. The regimen also cut the risk of distant metastasis or death by 38% compared with Keytruda by itself.

Moderna planned to present these detailed phase 3 trial results at the European Society for Medical Oncology conference this weekend. Investors have viewed the targeted vaccine as a potential breakthrough that could extend to other forms of cancer, providing Moderna with a critical commercial product beyond its existing pipeline of vaccines for Covid-19, the flu, and respiratory syncytial virus.

High expectations for the product contributed to a significant increase in Moderna's share price earlier in the year. As of Thursday afternoon, the stock had risen more than 530% year-to-date.