Moderna's stock price nearly doubled in premarket trading Wednesday after the company and partner Merck announced that their experimental personalized mRNA cancer vaccine met key endpoints in a large Phase 3 trial for melanoma.

Shares of Moderna rose as much as 95 percent in early trading following the news, marking one of the sharpest single-day gains in the company's history. The surge reflects investor enthusiasm for the first successful late-stage study of any mRNA-based cancer therapy.

The trial tested intismeran autogene, Moderna's individualized mRNA vaccine, combined with Merck's Keytruda immunotherapy in more than 1,100 patients with high-risk or advanced melanoma whose tumors had been surgically removed. The combination significantly extended the time patients remained free of cancer recurrence and reduced the risk of the disease spreading to distant sites compared with Keytruda alone.

These results represent a major validation of Moderna's mRNA platform beyond its COVID-19 vaccine. The personalized approach analyzes a patient's tumor mutations to create a custom vaccine designed to train the immune system to recognize and attack remaining cancer cells.

Moderna and Merck plan to seek regulatory approval based on the data, with potential market entry targeted for 2027. The outcome also boosts prospects for applying the technology to other cancers where similar personalized strategies could improve survival rates.

The announcement comes as Moderna works to diversify its revenue streams amid declining demand for its COVID-19 shots. Positive oncology data provides a clear path forward for the company's mRNA technology in a high-value therapeutic area.

Analysts noted that the trial's success could accelerate broader adoption of mRNA therapeutics in oncology, potentially reshaping treatment standards for melanoma and beyond. Merck's Keytruda has long been a cornerstone of immunotherapy, and pairing it with the vaccine appears to deliver additive clinical benefit.

The market reaction underscores strong private-sector momentum in biotechnology innovation. Shares of Merck also rose in premarket trading, though by a more modest amount, reflecting its established position in the partnership.