Moderna Closed Up 177% on the First mRNA Cancer Vaccine Win. The Effect Size Is Still Unpublished

UPDATE, 4:45pm ET, the settled numbers: Moderna closed at $174.38, up 176.97%, the largest one-day gain in its history; the prior record was 27.81% in February 2020, in the week the market first connected the company to a COVID vaccine. 191 million shares traded. Merck closed at $152.20, up 12.60%. After hours the stock was still climbing, $186.58 at 4:39pm, an extended-hours reading that will move overnight. The morning figures below stand as written, each with its timestamp. For what the day did to the weekly option chain, see what $1,000 of Tuesday's $80 calls became.

TL;DR

• Moderna closed at $174.38 on August 19, up 176.97% from Tuesday's $62.96: its biggest one-day gain on record, nearly tripling the stock in a session.
• The cause: intismeran autogene plus Keytruda met both endpoints of the Phase 3 INTerpath-001 trial in 1,137 patients with fully resected stage IIB-IV melanoma. It is the first mRNA-based cancer therapy ever to pass a late-stage trial.
• The topline release does not contain a hazard ratio. "Met both endpoints" establishes the direction of the result. How big the improvement is comes out at a medical meeting, and buyers at $174 are assuming a large one.
• Moderna splits this drug 50/50 worldwide with Merck. Barclays' estimate of roughly $3 billion in melanoma sales by 2035 comes nowhere near covering the ~$44.5 billion of market cap added today. The market is paying for the other eight trials.
• Fourteen days ago the FDA approved Moderna's flu vaccine. The platform has now been validated twice in a month, in two different diseases.

Why Is Moderna Stock Up Today?

Moderna and Merck announced that their personalized melanoma vaccine met both endpoints of its Phase 3 trial, the first mRNA cancer therapy ever to succeed in a late-stage study, and the stock closed at $174.38, up 176.97% from Tuesday's $62.96, per stockanalysis.com and CNBC: the largest single-day gain in the company's history. The move built all day. Shares crossed +57% in early premarket trade, went through +100% before the bell, opened around $121.90 per Forbes, printed a $176.66 intraday high, and settled at the close still near the top of the range. Merck closed at $152.20, up 12.60%, on the same news.

The morning reads that follow are labeled with their timestamps; the headline numbers above are the settled close.

The Board

A 177% day built on two words, "endpoints met". The number behind them is still unpublished.

What the Trial Showed

INTerpath-001 enrolled 1,137 patients whose stage IIB-IV cutaneous melanoma had been completely removed by surgery, randomized 2:1. One arm got intismeran autogene, formerly mRNA-4157 or V940, at 1mg every three weeks for up to nine doses, alongside Merck's Keytruda. The control arm got Keytruda alone, the current standard in this setting. Treatment ran about 56 weeks.

The combination beat Keytruda alone on recurrence-free survival, the primary endpoint, and on distant metastasis-free survival, the key secondary: whether the cancer comes back at all, and whether it spreads somewhere else in the body. Safety was consistent with earlier studies, with no new signals. The principal investigator, Prof. Georgina Long, called it a potential new treatment paradigm for adjuvant melanoma, and for once the framing is proportionate: no individualized neoantigen therapy and no mRNA cancer therapy had ever produced a positive Phase 3 before this morning.

The drug itself is the remarkable part. Intismeran is built one patient at a time: Moderna sequences the tumor, picks up to 34 mutations specific to that patient, and manufactures an mRNA shot that teaches the immune system to hunt cells carrying them. Melanoma is the proving ground because it is common and mutation-rich: the American Cancer Society counts about 112,000 new US cases and 8,510 deaths a year.

The Missing Number

The press release says both endpoints were met with "statistically significant and clinically meaningful" improvements. It does not say by how much. No hazard ratio, no percentages, no survival curves. Those arrive at an upcoming international medical meeting, and the companies say they will engage regulators on filing in the meantime.

The best available prior is the Phase 2b study, KEYNOTE-942, whose five-year data landed at ASCO in June: a 49% reduction in the risk of recurrence or death (HR 0.51) and a 59% reduction in distant metastasis or death, against Keytruda alone in a higher-risk population. If the Phase 3 effect lands anywhere near that, today's repricing will look conservative. Phase 2 effects also routinely shrink in Phase 3, this trial includes earlier-stage (IIB) patients where the benefit may be thinner, and a trial can be statistically positive with an effect half that size.

I think the repricing is a rational response to the direction of the result. Whether $174 survives the medical meeting depends on a number nobody outside the two companies has seen.

The Arithmetic of a $44 Billion Day

Moderna started today worth about $25.1 billion. It closed worth $69.6 billion.

Melanoma alone does not get you there. Barclays analysts put the melanoma opportunity around $3 billion in sales by 2035, per CNBC, and Moderna keeps half: the program is a 50/50 worldwide profit and cost split with Merck, who paid $250 million in 2022 to opt in. Half the profits on $3 billion of revenue, a decade out, is worth a few billion dollars of market cap today if you are feeling generous.

The other forty billion is the read-through. INTerpath is a nine-trial program: Phase 3s and Phase 2s running in lung, bladder, kidney, pancreatic and gastric cancer, every one of which just got more likely to work, because the platform question ("can an mRNA shot built from a tumor's own mutations actually prevent recurrence?") now has a Phase 3 answer. Leerink's Mani Foroohar had called this readout a make-or-break event for Moderna's valuation, per Forbes. It broke the right way, and the market repriced the platform rather than the drug.

Two things temper the euphoria, and I would hold both. Overall survival data does not exist yet; the study continues. And a therapy manufactured individually for every patient has never been produced at commercial scale: the cost and turnaround of making one drug per person is the operational question approval would force, and this release says nothing about it.

Fourteen Days, Two Verdicts

On July 31 I wrote that the whole company rested on August 5, the FDA's decision date for the flu vaccine. The approval came on schedule: mFLUSIVA, cleared August 5 for adults 50 and up on the strength of a 40,805-patient trial. The stock barely moved on it. I had the right thesis, a pipeline company priced on approvals rather than earnings, and picked the smaller of the two events that would prove it.

The sequence since is worth laying out plainly. This is a stock that traded at $29.81 on January 2, per Forbes. It came into its Q2 report up 83% on the year, still burning $782 million a quarter against $145 million of revenue. Then a flu approval on August 5, and a cancer-vaccine Phase 3 win on August 19. The bear case was always that the platform had one product, COVID, in permanent decline. That case has now lost twice in a month.

What comes next has dates attached loosely: the full data at a medical meeting, an FDA filing after regulator engagement, overall survival readouts later, and the lung-cancer trials behind melanoma in the queue. Today's scheduled calendar of retail earnings and Fed minutes lost the morning to a press release nobody had on the board.

The One-Line Read

The first mRNA cancer therapy just passed a Phase 3 trial, and Moderna closed up 177% before the effect size is public. The direction is proven. Whether $174 holds now rests on how big the benefit turns out to be.