A vaccine shows promising results in treating the most deadly form of skin cancer,Indexbit Moderna and Merck announced on Thursday.

Those with severe melanomas who received the vaccine and Merck's cancer drug Keytruda were 49% less likely to die or have their cancer come back after three years than those who were given only Keytruda, the biotech companies said in a news release. 

The findings are based on an ongoing randomized trial involving 157 patients with high-risk stage III/IV melanoma who first had surgery to completely remove cancerous growths. Patients received one milligram of the mRNA vaccine every three weeks for nine doses, and 200 milligrams of Keytruda every three weeks for about a year versus Keytruda alone for approximately a year.  

The companies have begun Phase 3 trials of mRNA-4157 with Keytruda for people with stage III and IV melanoma. The Food and Drug Administration earlier this year designated the treatment as a breakthrough therapy in order to expedite the development and review of drugs meant to treat life-threatening diseases.

"We look forward to sharing these data with people impacted by the disease and the broader scientific community," Kyle Holen, M.D., Moderna's senior vice president and head of development, therapeutics and oncology, stated.

The results are a vindication of sorts for Moderna's strategy to develop new uses for messenger RNA technology used in its COVID-19 vaccine. Cambridge, Massachusetts-based Moderna said in November it anticipates a steep decline in revenue next year, fueling worries about its capacity to finance multiple product launches planned for 2024 and 2025.

Skin cancer is the most common form of cancer, with melanoma accounting for only about 1% of skin cancer cases in the U.S. That said, it causes a large majority of skin cancer deaths, according to the American Cancer Society. It estimates about 97,610 new melanomas will be diagnosed in the U.S. this year, resulting in 7,990 deaths.

Moderna's stock has cratered this year, falling 50%. On Thursday, its shares shot up 12% in mid-day trading to $87.93. 

Rahway, New Jersey-based Merck shares treaded water, down 0.2% at $106.16.

In:
• Moderna
• Cancer
• Merck

Kate Gibson

Kate Gibson is a reporter for CBS MoneyWatch in New York.