Moderna (MRNA) shares fell as much as 25% on Thursday, despite positive cancer vaccine data. The shot cut melanoma recurrence or death risk by 42% in certain patients.

Partial data leaked before the full release. Even after the drop, the stock was up more than 530% for 2026 as of Thursday afternoon, CNBC reported.

How High Had the Bar Been Set for the Cancer Vaccine?

Merck, a much larger drugmaker, slipped about 1% and is up nearly 41% this year. In contrast, Moderna’s 2026 stock rally tops 530%.

BMO Capital Markets analyst Evan Seigerman said the selloff likely reflects outsized hopes going into the release. He did not read it as a verdict on whether the combination works.

Moderna fell sharply as expectations remain high. Source: TradingView

Meanwhile, UBS analysts called the results strong, adding that expectations may explain the reaction.

Intismeran autogene is a personalized shot aimed at mutations in an individual’s tumor. It is paired with Keytruda, Merck’s immunotherapy.

About 82% of patients on the combination were alive without recurrence at two years, versus 70% on Keytruda alone. The combination also cut the risk of distant spread or death by 38%.

Can One Melanoma Win Justify the Rest of the Rally?

However, the trial covered only one tumor type. Dean Li, president of Merck Research Laboratories, acknowledged more work is needed to prove the shot across cancers.

The companies are testing it in other tumors, including lung, bladder, and kidney cancers.

Success there could give Moderna a commercial product beyond its Covid-19, flu, and respiratory syncytial virus (RSV) vaccines.

Manufacturing is the catch, because each personalized dose can take six weeks to produce.

Personalized vaccines also depend on tumor sequencing, a niche BeInCrypto has covered as a diagnostics investment opportunity.

Still, Merck CEO Robert Davis told CNBC the company believes it can cut that wait, which would reach patients faster.

For now, the companies say it is too early to judge overall survival. Full phase 3 results are set for the European Society for Medical Oncology (ESMO) conference this weekend.

The next test for the sector is whether personalized medicine can be made fast enough to meet investor expectations.

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