US pharmaceutical companies Moderna and Merck released Phase 3 clinical trial results on the 22nd (local time) showing that their personalized messenger RNA (mRNA) cancer vaccine reduced the risk of recurrence and death in high-risk melanoma patients after surgery by 42%.

While the data were generally positive, the stock price plummeted as the announcement—coming after a surge in August when news of positive Phase 3 results first broke—fell short of heightened market expectations amid an embargo breach controversy. 

According to press releases from the two companies, patients who received "Intismeran," the vaccine co-developed by Moderna and Merck, in combination with Merck's immunotherapy drug Keytruda experienced a 42% lower risk of recurrence or death compared to those treated with Keytruda alone.

The hazard ratio (HR) is 0.58, meaning that the instantaneous risk of recurrence or death for the combination therapy group at any given time was 58% that of the monotherapy group.The 2-year recurrence-free survival rate was 82.2% for the combination group and 70.0% for the monotherapy group.Additionally, the risk of distant metastasis or death was shown to decrease by 38% (hazard ratio 0.62). 

Intismeran is a personalized mRNA vaccine manufactured by analyzing a patient's own tumor mutations. The Phase 3 trial involved 1,137 patients with stage 2B to 4 melanoma whose tumors had been completely removed by surgery, divided in a 2-to-1 ratio and followed with treatment and tracking for 24.6 months.

Treatment-related adverse events occurred in 95.8% of the combination group and 90.0% of the monotherapy group, with grade 3–5 adverse events standing at 14.2% and 13.4%, respectively.The two companies stated that no new safety signals were observed. 

Overall survival data are not yet mature, but a positive trend was observed. Both companies are in discussions with regulatory authorities. 

The data were originally scheduled to be unveiled on the 24th at the European Society for Medical Oncology (ESMO) congress in Madrid, Spain. 

However, after the results were posted early on the medical news site Oncology Central that afternoon, the two companies and the society released the data ahead of schedule. The society stated that it is investigating the breach of a prior confidentiality agreement. 

Along with the leak, Moderna's stock closed down 17.57% at $202.63 on the New York Stock Exchange. During the session, it plunged by more than 25% at one point. Moderna, which had skyrocketed 177% in a single day on August 19 following news of the Phase 3 trial's success, closed at $245.81 the previous day after hitting a 52-week high ($254.48) during intraday trading. Co-developer Merck also fell by 1.8%.

On Wall Street, reactions indicated that inflated expectations, rather than the data itself, were the problem. Michael Yee, a pharmaceutical and biotechnology analyst at UBS, called the data "solid," noting that the decline was an anticipated "sell-the-news" reaction. US financial media outlet MarketWatch reported that the recurrence and death hazard ratio of 0.58 was in line with or slightly lower than Wall Street expectations.

However, investment bank TD Cowen pointed out that the worsened results between the mid-stage and late-stage trials could mean a lower likelihood of success in cases where cancer has spread throughout the body or in "more challenging" tumors.The firm assessed that while the data figures are positive, they fell short of the market's elevated expectations.

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