Moderna and Merck said their experimental personalized mRNA cancer vaccine met its main goals in a phase 3 trial, cutting relapses and the spread of disease in patients who had undergone surgery for melanoma, according to 20minutos.es. The announcement, made on August 19, covered a study of 1,137 patients and set off an outsized reaction on Wall Street, where Moderna's shares jumped as much as 177% in a single session.
The result marks the first time a personalized mRNA cancer vaccine has cleared a phase 3 trial, the last major stage of testing before a company can seek regulatory approval. The two companies split profits and costs on the program evenly, so both stand to gain if the technology holds up.
Why it matters
The stakes extend well beyond one treatment. Merck sells Keytruda, the world's best-selling medicine, which brought in roughly $32 billion in 2025, 20minutos.es reports. Key patent protections on that drug begin to lapse in 2028. A successor arriving around that same window could determine whether Merck replaces its flagship revenue or watches it erode.
Bank of America has sketched a scenario in which the new treatment reaches $54 billion in annual sales, according to 20minutos.es — a figure that would surpass Keytruda's current peak. Morningstar is far more conservative, projecting combined sales of $16.8 billion by 2035. The gap between those estimates reflects how much remains unproven.
The trial also validates a scientific approach that had eluded the pharmaceutical industry for years. Cancer vaccines have long been a target; this is the first personalized mRNA version to succeed at this stage.
How the vaccine works
The treatment, called intismeran autogene, starts with a sample of a patient's tumor. Researchers analyze it to identify mutations that set the cancer apart from healthy cells. That information guides the design of an mRNA molecule that instructs the body to recognize specific features of the tumor and mount a defense against it.
It uses the same platform that allowed COVID-19 vaccines to be developed quickly, now aimed at a different purpose. The vaccine is not designed to stop a healthy person from developing cancer. It is given to patients who have already had surgery, in combination with Keytruda, to reduce the odds that the disease returns.
Earlier data had already pointed in a promising direction. Last summer, the companies reported that after five years of follow-up in a phase 2b trial, the combination lowered the risk of relapse or death by 49% compared with Keytruda alone, according to 20minutos.es. The phase 3 trial has now confirmed a statistically significant improvement, though full figures have not been released and it is not yet clear whether the treatment extends patients' lives.
The manufacturing problem
Making a different vaccine for every patient is a formidable logistical challenge. Each dose requires analyzing a tumor, designing and producing a bespoke formula, and delivering it on time. Doing that for hundreds of participants in a trial is a different problem from doing it for tens of thousands of patients.
Cost adds another obstacle. Some analysts put the full course of treatment at around $475,000 per patient, a price that raises hard questions about how many health systems could absorb it, 20minutos.es reports.
Morningstar estimates that about 30,000 patients a year across the United States and the European Union might match the profile of the population studied in melanoma. Moderna and Merck are already testing the same technology in other cancers, including lung, kidney and bladder tumors, across nine phase 2 and phase 3 trials.
Lung cancer is where the business could change scale entirely. In just one of the indications under study, Morningstar identifies more than 100,000 potential patients in the US and Europe — more than three times the melanoma figure. If the approach proves out in additional tumor types, the pool of eligible patients could keep expanding.
What to watch
The next test is the detailed publication of the phase 3 results and their review by health regulators, steps that could open the door to the first approvals in 2027.
