Moderna shares dropped as much as 25% on Thursday following a leak of partial data regarding its personalized cancer vaccine, intismeran autogene, developed in partnership with Merck. Despite the stock decline, the full data released later that day showed positive results relative to Wall Street expectations, demonstrating significant efficacy in treating melanoma when paired with Merck's immunotherapy Keytruda. The clinical trial results indicated that the combination therapy reduced the risk of recurrence or death by 42% compared to Keytruda alone. Furthermore, approximately 82% of patients receiving the vaccine alongside Keytruda remained alive without cancer returning at two years, a marked improvement over the 70% survival rate for those on Keytruda monotherapy. The treatment also exhibited milder toxicity profiles compared to other standard cancer treatments. Analysts and company executives characterized the data as clinically meaningful and a potential breakthrough, noting that the stock reaction likely stemmed from inflated market expectations rather than poor performance. Moderna CEO Stéphane Bancel highlighted the significance of this development for patients and noted that regulatory filings for approval are nearing completion, with hopes for market entry next year. While the current focus is on melanoma, Merck and Moderna are already expanding trials to include other tumor types such as non-small cell lung cancer and bladder cancer. The personalized nature of the vaccine requires a six-week manufacturing timeline, though Merck's CEO has expressed confidence in shortening this process to increase patient accessibility.