Moderna, Merck Shares Rally After Trial Shows Vaccine Success in Preventing Melanoma From Returning

By Robb M. Stewart

Shares of Moderna and partner Merck were up strongly ahead of the opening bell after the pair said an experimental mRNA-based vaccine succeeded in preventing cancer from coming back or spreading in a study of high-risk melanoma patients.

In premarket trading, Moderna's shares were 73% higher at $108.71 on Nasdaq, building on a rise of 38% over the last three months through Tuesday's close.

Merck was up 7% at $144.60 on the New York Stock Exchange, after climbing 18% over the last three months.

Merck and Moderna said the late-stage trial, which studied a novel investigational mRNA-based individualized neoantigen therapy in combination with Merck's cancer immunotherapy Keytruda met its main goal of extending the time before cancer returns in high-risk patients.

The study also met a secondary goal of preventing the disease from spreading to different organs.

The result represents the first positive phase 3 readout for an individualized neoantigen therapy and for an mRNA-based cancer therapy, as well as the first phase 3 study to demonstrate a clinically-meaningful improvement over Keytruda alone, for patients with resected melanoma, the companies said.

The data will be presented at an upcoming international medical meeting and shared with regulatory authorities, they said.

Write to Robb M. Stewart at robb.stewart@wsj.com

(END) Dow Jones Newswires

August 19, 2026 07:37 ET (11:37 GMT)