Moderna Stock Soars 135% After Phase 3 mRNA Cancer Vaccine Melanoma Win

On Wednesday, August 19, 2026, Moderna, Inc. (NASDAQ: MRNA) and Merck & Co. (NYSE: MRK) announced positive topline results from the Phase 3 INTerpath-001 trial of their personalized mRNA cancer vaccine intismeran autogene combined with KEYTRUDA (pembrolizumab) in patients with completely resected stage IIB–IV melanoma. Moderna stock closed the prior session at $62.96 and surged more than 135% during the day, reaching an intraday high of $163.47 before settling near $153 — one of the largest single-day rallies in the company’s history.

Editor’s note: This article draws on joint statements from Merck and Moderna, Reuters reporting, and market data for August 19, 2026. The companies have not yet released full efficacy statistics; figures may be updated at a future medical conference.

What the companies announced

Merck and Moderna said the trial met its primary endpoint of recurrence-free survival (RFS) and a key secondary endpoint of distant metastasis-free survival (DMFS) at a pre-specified interim analysis.

At that readout, intismeran plus Keytruda as adjuvant therapy — given after surgical removal of the tumor — showed statistically significant and clinically meaningful improvements in both RFS and DMFS compared with Keytruda alone in patients with completely resected stage IIB, IIC, III, or IV cutaneous melanoma who had not received prior systemic therapy.

The companies called the result a milestone on several fronts:

First-of-its-kind claim	Detail
Individualized neoantigen therapy (INT)	First positive Phase 3 readout for this class
mRNA cancer therapy	First positive Phase 3 for an mRNA-based cancer treatment
Adjuvant melanoma	First Phase 3 to show a meaningful benefit over Keytruda monotherapy after surgery

The study will continue to evaluate additional endpoints, including overall survival (OS), in line with the trial protocol.

How intismeran works

Intismeran autogene (also known as V940 or mRNA-4157) is an investigational individualized neoantigen therapy. After a patient’s tumor is removed, researchers sequence it to identify unique mutations. Moderna then manufactures a personalized mRNA vaccine encoding up to 34 neoantigens tailored to that patient’s cancer profile.

The vaccine is designed to train the immune system to recognize and attack residual cancer cells. It is administered alongside Keytruda, Merck’s blockbuster anti-PD-1 immunotherapy, which helps T cells overcome tumor defenses.

Unlike some personalized cell therapies that require harvesting and modifying a patient’s own immune cells, intismeran uses an off-the-shelf manufacturing model built on mRNA technology — a approach Moderna CEO Stéphane Bancel has said could support broader scale-up and lower costs relative to bespoke cell products.

Trial design: INTerpath-001

Parameter	Detail
Trial name	INTerpath-001 (NCT05933577)
Patients enrolled	1,137
Randomization	2:1 — combination vs. Keytruda alone
Population	High-risk resected stage IIB–IV cutaneous melanoma
Combination arm	Intismeran 1 mg every 3 weeks (up to 9 doses) + Keytruda 400 mg every 6 weeks (up to 9 cycles)
Control arm	Keytruda alone for approximately one year
Treatment duration	Up to ~56 weeks, or until recurrence or unacceptable toxicity

Melanoma is the deadliest form of skin cancer. More than 1.5 million people worldwide are diagnosed annually, and adjuvant treatment after surgery is critical for patients at high risk of recurrence.

Building on Phase 2 data

Wednesday’s Phase 3 readout extends earlier evidence from the Phase 2 KEYNOTE-942 / mRNA-4157-P201 study. At the 2026 ASCO Annual Meeting, the partners reported five-year follow-up showing the combination reduced the risk of recurrence or death by 49% (hazard ratio 0.51) and the risk of distant metastasis or death by 59% (HR 0.411) versus Keytruda alone.

In 2024, Merck and Moderna held preliminary talks with regulators about seeking approval based on Phase 2 data but received discouraging feedback from the U.S. Food and Drug Administration (FDA). With a full Phase 3 success in hand, the companies now plan to engage regulators on approval filings with a substantially larger dataset.

Merck and Moderna said they will present detailed Phase 3 results at an upcoming medical meeting. Full efficacy numbers — including hazard ratios and median follow-up — were not disclosed in the topline announcement.

Safety profile

The companies reported that the safety profile of intismeran plus Keytruda was consistent with prior studies and that no new safety signals emerged during INTerpath-001. The trial protocol allowed treatment for up to roughly one year unless disease recurred or toxicity became unacceptable.

Moderna stock: market reaction

Investors treated the readout as a potential inflection point for Moderna beyond its COVID-19 vaccine franchise. Shares had traded near multi-year lows before the announcement, reflecting weak post-pandemic vaccine demand and a stretched product pipeline.

Metric	Value (Aug. 19, 2026)
Prior close	$62.96
Premarket	Up roughly 91% to about $120
Intraday high	$163.47
Approximate daily gain	>135% (reports ranged up to ~143% at the close)
Volume	Tens of millions of shares — sharply above average

Merck shares moved more modestly, reflecting that Keytruda is already a multibillion-dollar product and Merck’s broader portfolio dilutes the impact of any single adjuvant indication.

Analysts including RBC Capital Markets characterized the result as validating Moderna’s mRNA oncology platform, with potential upside across additional tumor types if later trials succeed.

What comes next

The partners outlined several near-term steps:

1. Present full data at a major oncology conference (date not yet announced).
2. Engage global regulators — including the FDA — on potential marketing applications for the adjuvant melanoma indication.
3. Continue INTerpath-001 to assess overall survival and other secondary endpoints.
4. Advance broader pipeline — Merck and Moderna are also studying intismeran in non-small cell lung cancer and other solid tumors.

Bancel told reporters the companies had not yet set a price for intismeran, noting the Phase 3 data had only recently become available. Pricing, reimbursement, and manufacturing capacity will be closely watched given the personalized nature of each dose.

For patients and clinicians, regulatory review timelines remain uncertain. A positive Phase 3 topline does not guarantee approval, and the FDA may request additional follow-up — particularly on overall survival — before clearing the combination for routine adjuvant use.

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Discussion

A single trial readout reshaped how markets value an entire technology platform — but the clinical and access questions are only beginning.

1. Does a 135% one-day jump in Moderna stock reflect a real shift in the company’s long-term value, or a short-term repositioning trade?

Moderna’s COVID-era revenue has faded, and oncology was always the strategic bet. If you hold biotech shares, do you treat Wednesday’s rally as confirmation — or as a moment to reassess risk?

2. Personalized mRNA cancer vaccines could change adjuvant melanoma care — but each dose is built from an individual tumor’s mutations. Who should get access first if regulators approve the combination, and what would fair pricing look like?

Share where you think the line should be drawn between innovation rewards and patient affordability.

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This article is news and general health information, not personal medical or investment advice. Clinical trial results are preliminary until peer-reviewed data are published and regulators complete their reviews. Consult a qualified healthcare provider or financial adviser before making treatment or investment decisions.