The news: Merck and Moderna’s personalized mRNA cancer vaccine showed it could delay the return of melanoma in a Phase 3 trial when combined with Merck’s Keytruda. Patients who had melanoma surgically removed and received the experimental drug alongside Keytruda had significantly improved recurrence-free survival compared with those on Keytruda alone.

The drugmakers called it the first positive Phase 3 result for an mRNA-based cancer treatment and plan to present full data while engaging regulators on filings. Shares of both companies surged after the announcement Wednesday, with Moderna up 125% and Merck rising as much as 11%, per CNBC.

Why it matters: Drugmakers have spent decades trying to develop cancer vaccines tailored to individual patients’ tumors—the Phase 3 results provide the strongest validation yet that the approach can work.

Merck and Moderna are not alone in studying individualized cancer therapies, though the two have nine total mRNA trials running in lung, bladder, and kidney cancers. Meanwhile, BioNTech and its partner Genentech are developing mRNA-based personalized cancer vaccines in pancreatic, colorectal, and head and neck cancers. Earlier-stage trials have also produced positive results, including a personalized pancreatic cancer vaccine by Memorial Sloan Kettering researchers and another showing prolonged survival in patients with brain cancer at Washington University School of Medicine.

Merck and Moderna’s breakthrough comes in what is already one of pharma's biggest and fastest-growing categories. Global spending on cancer medicines reached $252 billion in 2024 and is projected to hit $441 billion by 2029, per IQVIA. Melanoma itself is expected to account for about 112,000 new US diagnoses and more than 8,500 deaths in 2026, per Merck.

Implications for pharma and healthcare companies: Cancer treatment already includes therapies designed to prevent recurrence after surgery, but a personalized vaccine would add a new approach. If Merck and Moderna win approval, patient and provider education will need to explain a genuinely new mechanism: a treatment manufactured using a patient’s own tumor sample rather than a standard mass-audience therapy. That will require clear communication around eligibility, timelines, and what treatment involves. A more complex treatment process could make roll out slower even after approval—potentially adding to existing patient and family frustration over how long new cancer therapies take to reach them.

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