Merck Surges 12.6% After Its Cancer Vaccine With Moderna Clears a Phase 3 Trial

Merck rose 12.6% on Wednesday, closing at $152.20, after the company and its development partner Moderna said an experimental cancer vaccine succeeded in a late-stage melanoma study. The buying was heavy. Trading volume ran 3.9 times the stock’s 20-day average, and the close carried Merck above the top of its three-month price range.

The first Phase 3 win for an mRNA cancer vaccine

The two companies reported positive topline results from a study called INTerpath-001. It tested intismeran autogene, an mRNA therapy built to match each patient’s own tumor mutations, given alongside Merck’s established immunotherapy Keytruda. Each dose is made after a patient’s tumor is sequenced, and the therapy is designed to train the immune system against as many as 34 mutations specific to that cancer. The trial enrolled 1,137 patients whose stage IIB-IV melanoma had been surgically removed. According to Merck and Moderna, the combination met its primary goal of lengthening the time patients lived without their cancer returning, and it met a secondary goal of delaying the spread of the disease to distant organs. Both results beat Keytruda given on its own.

The companies described the outcome as the first Phase 3 success for an individualized neoantigen therapy and for any mRNA-based cancer treatment. Safety, they said, was in line with earlier studies, with no new warning signs. Detailed figures were not released. Merck and Moderna said they would present the full data at a medical meeting and open discussions with regulators about filing for approval.

What a Keytruda partner means for Merck

The market reaction was far larger for Moderna, whose shares nearly tripled as investors reweighed a pipeline that had struggled since the pandemic years. For Merck, the readout lands closer to the core of the business. The stakes are different. Keytruda is the company’s top-selling drug and faces the loss of patent protection late this decade. A vaccine that adds to Keytruda’s benefit gives Merck a way to extend that franchise into a new patient group, which is why a single melanoma trial moved a company of Merck’s size. The two companies are also running the same combination in a late-stage lung-cancer study, so the melanoma result reads as an early signal for a wider program.

A rally that began before Wednesday

The one-day jump extended a climb that was already in motion. The trend was not new. Merck had gained 20.5% over the prior 30 days, and Wednesday’s close left the stock 39% above its lowest point of the past three months. The move also cleared the top of that range outright, marking a fresh high within the window. Volume at nearly four times the usual pace set the trial result apart from ordinary drift, pinning the day’s gain to the announcement itself.

The data and the filings still to come

Two events will shape the story from here. The first is the release of the detailed trial data at an international medical meeting, where oncologists will judge the size of the benefit for themselves rather than from a topline summary. The second is a regulatory submission, the step that would turn a successful study into a product doctors can prescribe. Merck and Moderna have signaled both are coming. Neither carries a public date yet.

This is a general-market summary for information only — not investment advice, and not a recommendation regarding any security.