Moderna’s stock soared Tuesday after the COVID-19 vaccine maker detailed progress in developing a preventive shot for a deadly form of skin cancer.

The company said a possible melanoma vaccine it is studying with pharmaceutical giant Merck fared well in a small study of patients who had the cancer surgically removed.

The drugmakers said a combination of the vaccine and Merck’s immunotherapy Keytruda led to a statistically significant improvement in survival before the cancer returned in patients with advanced melanoma.

“We are very excited, we are moving very quickly with Merck onto phase 3 for this study,” Moderna CEO Stephane Bancel told CNBC Tuesday morning.

Phase 3 is generally the largest and most expensive stage of clinical research before regulators review a potential drug for approval.

Moderna developed one of the most popular vaccines used to protect patients against COVID-19, and the drugmaker brought in more than $3 billion from its Spikevax in this year’s third quarter.

But vaccine use has slowed, and Moderna depends on Spikevax for nearly all its revenue.

Like Spikevax, the potential skin cancer vaccine uses mRNA technology. It trains a patient’s immune system to recognize and respond specifically to mutations in the DNA of the patient’s tumor.

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In a mid-stage clinical trial involving 157 patients, researchers compared the vaccine-Keytruda combination with Keytruda alone.

Keytruda, Merck’s top seller, primes the body’s immune system to detect and fight tumor cells. Regulators have approved it to treat several types of cancer.

The patient group that took the potential vaccine and Keytruda saw a 44% reduction in the risk of death or the cancer returning, the companies said.

The treatments continued for about a year in both groups unless the disease came back or side effects became too severe.

Merck and Moderna expect to start a phase 3 study next year, and the companies say they intend to expand their approach to other tumor types.

Merck and Moderna established an agreement to work together in 2016, and the companies plan to share costs and profits in their collaboration. Merck also paid Moderna $250 million.

Shares of Cambridge, Massachusetts-based Moderna Inc. soared 23% to top $200 in midday trading while broader indexes climbed. Kenilworth, New Jersey-based Merck & Co. climbed less than 1%.