Moderna and Merck said Wednesday their personalized mRNA cancer vaccine met its main goals in a Phase 3 trial targeting melanoma, marking the first time a therapy of its kind has succeeded at that stage of testing. The news sent Moderna’s stock up more than 100% and lifted Merck shares as well, as investors bet on a new era for a company long defined by its Covid-19 vaccine.

The companies’ vaccine, called intismeran autogene, is built from a sample of a patient’s own tumor. It is designed to teach the immune system to recognize the specific mutations in that person’s cancer. In the trial, patients with high-risk melanoma, one of the deadliest forms of skin cancer, who had already had their tumors surgically removed received either the vaccine plus Merck’s immunotherapy Keytruda, or Keytruda alone.

The trial included 1,137 patients with high-risk melanoma, cases in which the cancer had grown deep or spread to nearby lymph nodes, or in some cases, to other parts of the body. All of them had already had their tumors removed by surgery before enrolling. Patients who got the vaccine alongside Keytruda went longer without their cancer coming back or spreading than those who got Keytruda alone, meeting the trial’s two main goals.

The companies haven’t released the exact numbers behind that improvement yet, saying only in press releases on Wednesday the results were “statistically significant and clinically meaningful.” They plan to share full data at an upcoming medical conference and bring the results to regulators.

The readout builds on earlier data from the same drug combination, which showed a 49% reduction in the risk of recurrence or death and a 59% reduction in the risk of distant metastasis or death, compared with Keytruda alone. Merck referenced those figures directly in Wednesday’s release. Fortune has previously covered how personalized cancer vaccines like this one work, and Moderna CEO Stéphane Bancel discussed the melanoma data’s earlier stages in an interview with Fortune last year.

Dr. Danish Nagda, an otolaryngologist who has treated head and neck melanoma patients and is founder and CEO of the healthcare startup Rezilient Health, told Fortune just how big this news is. For patients with advanced, stage three or four melanoma, five-year recurrence-free survival today runs around 20 to 35%, he said.

“This potentially doubles it,” Nagda said.

Bancel described the trial as validation of an idea the company has pursued for years.

“For many years, the idea of creating an mRNA treatment designed specifically for an individual patient’s cancer was aspirational. We are now helping turn that vision into a reality,” Bancel said. “Together with Merck, we have started to demonstrate the transformative potential of this technology to address critical unmet needs in the adjuvant melanoma setting.”

Dr. Dean Y. Li, president of Merck Research Laboratories, said the results were evidence for treating cancer earlier.

“By intervening earlier in the course of disease, when many cancers are considered most treatable, the goal of adjuvant therapy given after surgery is to increase the possibility of cure for more patients,” Li said. “We believe individualized neoantigen therapies have the potential to redefine how patients with completely resected stage IIB-IV melanoma are treated.”

“Today’s results represent a landmark moment for adjuvant melanoma treatment,” said Georgina Long, the trial’s principal investigator, medical director of Melanoma Institute Australia, and chair of melanoma medical oncology and translational research at the University of Sydney. “Intismeran in combination with pembrolizumab has the potential to establish a new treatment paradigm in the adjuvant melanoma setting, helping patients remain cancer-free for longer.”

The market reaction

Investors responded immediately to the news as Moderna’s stock more than doubled in early trading Wednesday, while Merck shares climbed as well. Merck is currently valued at roughly $371 billion and Moderna at around $62 billion.

“This makes Moderna a great acquisition target,” said Nagda, who sees the stock move as still behind where the platform’s value should land. “Moderna is still incredibly undervalued. It seems like a large increase, but it’s actually very much underestimating the value of a platform,” Nagda told Forutne. “Now that mRNA has been used in this way to go after melanoma, what stops us from going after other targets? I bet you over the course of the next 12 to 18 months, Moderna will be significantly higher than it is right now.”

Nagda trained at the University of Pennsylvania’s Perelman School of Medicine and completed his ENT residency at Washington University in St. Louis, where he treated patients with head and neck melanoma, often on combination immunotherapy regimens. He said the promise from this study comes from relaxed regulations that have helped move drugs forward, faster.

“This looks good for the Trump administration’s Operation Warp Speed, because this would not have existed without the mRNA vaccine coming out. This accelerated potentially a long-term solution for us to target cancers,” Nagda said, adding he doesn’t expect the treatment to face a difficult path to approval given how strongly oncologists are likely to embrace it for advanced melanoma patients. Fortune has reported on declining public trust in the FDA amid political interference, a backdrop against which any accelerated filing timeline for the vaccine would play out.

The results are promising

Nagda pointed to a factor he said gets little attention in coverage of the trial: rising skin cancer rates tied to climate change.

“Melanoma is not just an American issue. Australia has incredibly high rates of melanoma. It’s a big global issue, and it’s only going to get worse with climate change, as you continue to see more UV radiation and hotter climates,” he said. “Even right now, we’re seeing sunscreen rates going down. Melanoma is going to become more and more prevalent amongst Caucasians, but also amongst other ethnicities.”

Nagda pointed to the safety data as another reason for optimism. In earlier trial data, reactions resolved in about 80% of the 40 patients studied, he said, calling that figure “huge.”

“The side effect profile is minimal compared to a traditional therapeutic for patients with cancer,” Nagda said.

Nagda explained why the vaccine’s side effect profile differs so much from older cancer treatments. Traditional chemotherapy works by exploiting the fact that cancer cells mutate, replicate, and consume energy faster than healthy cells, he said—the goal is to kill the cancer before the drug kills the patient. The mRNA vaccine takes a different approach entirely.

“This is going directly after the cancer cells at a direct level, targeting a unique mutational fingerprint specific to that patient’s own tumor,” Nagda said. “It’s not just personalized across all patients. It’s personalized to the patient’s own tumor.” This is different than traditional chemotherapy, where “our goal is to kill the cancer before the drug kills the human.”

This story was originally featured on Fortune.com