Moderna's cancer vaccine hits its targets, but a data leak rattled investors and the stock tumbled

By Jaimy Lee

A 'sell-the-news reaction'? The experimental treatment helped prevent the return of cancer or death in melanoma patients by 42% after two years.

Moderna and Merck ended up sharing the Phase 3 results for their experimental cancer vaccine two days early.

Moderna and Merck's cancer vaccine helped prevent the return of melanoma or death by 42% after about two years in patients who participated in the high-profile Phase 3 clinical trial.

The therapeutic vaccine, called intismeran, is a groundbreaking new approach that makes use of the patient's own tumor to create a personalized treatment, which is then administered alongside Keytruda, Merck's blockbuster cancer drug.

Dean Li, president of Merck Research Laboratories, said the study represents "one of the most significant advances in melanoma treatment since the advent of immunotherapy," referring to the approvals of Keytruda and other immunotherapies like Bristol Myers Squibb's (BMY) Opdivo a decade ago.

The trial results were set to be announced Saturday at an important medical conference in Madrid, but Oncology Central, a cancer news site operated by the publishing giant Informa, prematurely published a story with the embargoed data, driving down the stocks of both companies on Thursday afternoon. Oncology Central did not respond to a request for comment. The conference lifted the embargo on Thursday afternoon after the leak.

Moderna shares (MRNA) closed 17.6% on Thursday, while Merck's stock (MRK) ended the day down 1.7%.

William Blair analyst Myles Minter questioned whether the stock declines were the result of a "sell-the-news reaction" or broader concern that there were no major differences in efficacy for patients with different mutational burdens in their tumors. Melanoma has a high mutational burden, which means immunotherapies work well against this kind of cancer. But much of the hope around the vaccine is that it will work in cancers with lower mutational burdens.

"That alone is a reason to wait for the [European Society of Medical Oncology] data presentation this weekend," he told investors.

The study enrolled about 1,100 patients with later-stage melanoma who first underwent surgery before receiving either intismeran and Keytruda or Keytruda alone.

One of the key data points is the hazard ratio, an important measure that shows how long patients live before the cancer comes back.

In the Phase 3 study, the hazard ratio was 0.58, which is on par with or slightly lower than what Wall Street analysts had expected. It's also similar to the hazard ratio in the smaller Phase 2 trial. A hazard ratio between 0.5 and 0.6 would be "a pretty good result," RBC Capital Markets analyst Trung Huynh said Wednesday.

That sentiment was echoed by BMO Capital Markets analyst Evan David Seigerman, who told investors that the "relative reduction in recurrence/death is clinically meaningful," even though it appears to have disappointed investors.

Another figure that investors pay attention to is overall survival. Moderna and Merck said that data were not yet mature but noted that there is a "favorable trend." They are continuing the Phase 3 study to collect data on overall survival.

With the latest data in hand, the companies now plan to pursue approval of the experimental treatment.

They are also still expected to participate in the presentation on Saturday in Madrid at the European Society of Medical Oncology's annual conference, which usually draws about 30,000 attendees. The conference had already selected the presentation for its presidential symposium, a slot reserved for medical studies that have the potential to change the standard of care.

Drugmakers and medical conferences often share an embargoed version of a study with members of the media, who agree not to publish or share the findings with anyone before an agreed-upon publication time.

Spokespeople for Moderna and Merck said the companies had no comment. A spokesperson for ESMO confirmed the breach and lifted the embargo. The presentation will still be released on Saturday "due to technical constraints."

Moderna's stock has been one of the top performers in the S&P 500 SPX this year, fueled by its announcement in August that the Phase 3 trial was successful, while Merck shares have hit several record highs since the announcement.

-Jaimy Lee

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10-22-26 1614ET