Moderna shares plummeted as much as 25% on Thursday after key data for its cancer vaccine, developed in partnership with Merck, was leaked. Although the full data subsequently released showed that the vaccine, when used in combination with Merck's immunotherapy Keytruda, reduced the risk of recurrence or death by 42% in certain melanoma patients, the share price was still affected. The vaccine, named intismeran autogene, was scheduled to have its late-stage clinical trial results presented at the European Society for Medical Oncology conference this weekend.