Moderna and Merck say their mRNA cancer vaccine cut death, recurrence by 42%

What happened

Moderna and Merck announced that their custom-made mRNA vaccine helped patients with melanoma, a very dangerous skin cancer. Compared with the standard treatment alone, the vaccine cut the risk of death or the cancer returning by 42 percent. The companies are already talking with health regulators to get the vaccine approved. The full results will be published in the New England Journal of Medicine.

Key numbers

• The Phase 3 trial (a large, late-stage test in people) included 1,137 patients with melanoma that had been removed by surgery.
• After two years, 82 percent of patients getting the vaccine plus Keytruda were alive without the cancer returning. Only 70 percent of patients getting Keytruda plus a placebo (a fake treatment) were.
• The vaccine lowered the risk of the cancer spreading to a new part of the body, or death, by 38 percent.
• An earlier five-year Phase 2 trial showed stronger results: a 49 percent drop in the risk of recurrence or death.
• Each vaccine can carry instructions for up to 34 mutations (changes in the genes) found in a patient's own cancer cells.

How the vaccine works

The vaccine is called intismeran, also known as mRNA-4157. Researchers compare the genes of a patient's cancer cells with healthy cells. They then pick out cancer-specific changes. The vaccine uses synthetic mRNA, a copy of genetic instructions, to teach the immune system (the body's defense system) to attack only the cancer cells. Keytruda is an existing cancer drug that helps the immune system fight tumors.

Why it matters

This result gives hope that mRNA vaccines, which were first made known for COVID-19 shots, could become a new way to treat cancer. Each vaccine is made for one patient's tumor, so it is a very different approach from most medicines. The effect was weaker than in the earlier Phase 2 trial, so experts will want to see the full data before drawing big conclusions.

What to watch

• Whether regulators approve the vaccine for melanoma patients.
• The full trial data in the New England Journal of Medicine.
• Results from the scientific conference in Madrid, where the data was first planned to be presented.
• Whether the vaccine works for other types of cancer.