Moderna shares exploded higher on August 19 after the biotechnology company and Merck reported a historic Phase 3 victory for their personalized melanoma treatment. Moderna stock climbed about 144% to $153.60 during morning trading, up from its previous close of $62.96.
The stock touched $163.01 at its intraday peak, representing a gain of approximately 159%. More than 83 million shares had traded by late morning, while Moderna’s market value rose to roughly $61 billion.
The announcement matters beyond Wall Street. It provides the strongest late-stage evidence yet that messenger RNA technology can be used to treat cancer, not only protect against infectious diseases.
Phase 3 trial involved 1,137 melanoma patients
The INTerpath-001 trial enrolled 1,137 patients with high-risk stage IIB, IIC, III or IV cutaneous melanoma. Their tumors had been completely removed through surgery, but they remained at risk of the cancer returning or spreading.
Patients were randomly assigned on a two-to-one basis to receive Moderna’s intismeran autogene treatment with Merck’s Keytruda or Keytruda alone. The study was randomized, double-blind and controlled with an active comparator and placebo.
The combination delivered statistically significant and clinically meaningful improvements in recurrence-free survival. It also improved distant metastasis-free survival, which measures how long patients remain alive without cancer spreading to distant parts of the body.
The official Phase 3 announcement identifies this as the first positive late-stage result for an individualized neoantigen therapy and an mRNA-based cancer treatment.
How the personalized cancer treatment works
Intismeran, previously known as V940 or mRNA-4157, is not a conventional vaccine given to healthy people. It is manufactured separately for each cancer patient using genetic information obtained from the person’s tumor.
Researchers identify unique tumor mutations and create an mRNA treatment containing instructions for as many as 34 cancer-related markers called neoantigens. The objective is to train the immune system to recognize and attack cells carrying those markers.
Keytruda blocks the PD-1 pathway that tumors can use to evade immune cells. In simple terms, intismeran helps the immune system identify the target, while Keytruda helps it maintain the attack.
Patients received one milligram of intismeran every three weeks for as many as nine doses. Keytruda was administered at 400 milligrams every six weeks for up to nine cycles, with total treatment lasting approximately one year.
Earlier results showed lasting benefits
The Phase 3 trial followed encouraging results from the smaller Phase 2b KEYNOTE-942 study. After five years, the combination was associated with 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.
Those percentages are from the earlier Phase 2b study, not the new Phase 3 trial. Moderna and Merck have not yet disclosed the Phase 3 risk-reduction figures, hazard ratios, absolute event rates or complete subgroup findings.
The companies reported no new safety signals, although this does not mean the treatment caused no side effects. Full data will be needed to assess serious reactions, treatment discontinuations and whether toxicity was higher than with Keytruda alone.
The trial is continuing to evaluate overall survival. The current result shows that the combination delayed recurrence and distant spread, but it does not yet prove that patients lived longer overall.
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Moderna and Merck shares surge
Moderna initially gained about 87% in premarket trading before the rally accelerated after the opening bell. The varying gains of 87%, 130%, 144% and more than 150% reported during the day reflected prices recorded at different times.
Merck shares advanced nearly 11% to about $149.54 and touched an intraday high of $151.72. The move followed an active period for the pharmaceutical company after Merck shares previously rallied ahead of quarterly results.
BioNTech gained approximately 23%, while Novavax rose close to 8% as investors reassessed the broader potential of mRNA technology and cancer vaccines.
The magnitude of Moderna’s move was far greater than its earlier earnings reaction. In February, Moderna stock gained following a $678 million revenue beat, although declining COVID-19 vaccine demand remained a concern.
Why the breakthrough matters financially
Moderna has been under pressure to prove that its mRNA platform can deliver commercially successful products beyond COVID-19. A cancer treatment could create a major new revenue stream and strengthen confidence in the company’s wider research pipeline.
The result is also significant for Merck. Keytruda and its related formulation generated approximately $8.4 billion in second-quarter 2026 sales, accounting for roughly half of Merck’s total quarterly revenue of $16.6 billion.
Moderna and Merck are evaluating intismeran through nine Phase 2 and Phase 3 studies. The program includes non-small cell lung, bladder and kidney cancers, although success in melanoma does not guarantee positive results in other tumors.
Approval and major questions remain
The companies plan to present the complete data at an international medical meeting and discuss possible approval applications with regulators. No filing date, approval timetable, price or commercial launch date has been announced.
Personalized manufacturing may also create challenges because every treatment must be designed from an individual patient’s tumor. Production time, cost, insurance coverage and access outside major cancer centers could influence its eventual use.
The treatment should not be described as a universal cancer cure. It was tested after surgery in a specific group of high-risk melanoma patients and reduced recurrence and distant spread compared with Keytruda alone. The complete Phase 3 presentation will reveal whether the size and durability of that benefit support Moderna’s extraordinary market rally.
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