Intismeran Plus Keytruda Cuts Melanoma Recurrence Risk 42% in Phase 3, but Moderna Shares Close Down 17.6%

Merck and Moderna on Thursday, Oct. 22, 2026 released the detailed Phase 3 results investors had waited for since August: intismeran autogene plus KEYTRUDA cut the risk of recurrence or death by 42% in patients with completely resected stage IIB-IV melanoma, and Moderna shares still closed down 17.6%.

The INTerpath-001 trial enrolled 1,137 patients with completely resected stage IIB-IV cutaneous melanoma and randomized them 2:1 to intismeran at 1 mg every three weeks for up to nine doses plus KEYTRUDA at 400 mg every six weeks for up to nine cycles, about one year, or to placebo plus KEYTRUDA. At the primary pre-specified intention-to-treat analysis, after a median follow-up of 24.6 months, the combination reduced the risk of recurrence or death by 42%, with a hazard ratio of 0.58 (95% confidence interval 0.45 to 0.75) and a two-sided p value below 0.001. It also reduced the risk of distant metastasis or death by 38%, with a hazard ratio of 0.62 (0.45 to 0.85) and p equal to 0.002. The two-year recurrence-free survival rate was 82.2% (79.3% to 84.8%) with the combination against 70.0% (65.0% to 74.5%) with KEYTRUDA alone, and the two-year distant metastasis-free survival rate was 88.5% (86.0% to 90.6%) against 80.2% (75.6% to 84.0%). Median recurrence-free survival and median distant metastasis-free survival were not reached in either arm.

A benefit that emerged after the immunization course

The timing inside the result matters. In the first six months, the combination was comparable with KEYTRUDA alone, with a recurrence hazard ratio of 0.99 (0.66 to 1.49) and a distant metastasis hazard ratio of 1.01 (0.58 to 1.79). After six months, following the intismeran immunization regimen, a pre-specified sensitivity analysis showed a 58% reduction in the risk of recurrence or death, a hazard ratio of 0.42, and a 50% reduction in the risk of distant metastasis or death, a hazard ratio of 0.50. In the modified intention-to-treat sensitivity population, the reductions were 49% for recurrence or death, hazard ratio 0.51, and 45% for distant metastasis or death, hazard ratio 0.55. Overall survival data are not yet mature; the companies reported a favorable trend only, and the study remains ongoing. Treatment-related adverse events occurred in 95.8% of patients on the combination (723 of 755) against 90.0% on KEYTRUDA alone (342 of 380), with grade 3 to 5 treatment-related events in 14.2% against 13.4%; the most common combination events were fever in 52.2%, injection site pain in 51.0% and fatigue in 38.5%, and the companies reported no new safety signals.

Dr. Dean Y. Li, president of Merck Research Laboratories, said: "INTerpath-001 is the first Phase 3 study to demonstrate a clinically meaningful improvement in RFS and DMFS over standard-of-care KEYTRUDA in patients with resected melanoma." Dr. Hussein Tawbi, a melanoma expert and trial investigator, said of the results: "This is highly statistically significant. It is not by chance." Intismeran is an individualized neoantigen therapy: a synthetic messenger RNA coding for up to 34 neoantigens drawn from the unique mutational signature of a patient's own tumor. The detailed results will be presented on Saturday, Oct. 24 at the European Society for Medical Oncology Congress 2026 in Madrid, in Presidential Symposium I as presentation LBA1, and have been accepted for publication in a leading medical journal. The companies said only that they are engaging with regulatory authorities; no filing date or approval claim was made.

Why positive data still produced a steep fall

The market reaction ran the other way. Moderna closed at $202.63 on Thursday, down $43.18, or 17.6%, from a previous close of $245.81, after falling much further during the session: it was last down 25.2% at $183.88 in intraday reporting, a move that wiped about $24 billion from its market value and was described as its steepest one-day percentage fall on record, with an intraday low of $180.80. Merck shares fell nearly 1% in the same reporting, after closing down about 0.7% in an earlier read. The sequence explains part of the violence: the results leaked on an oncology website earlier on Thursday, the European Society for Medical Oncology confirmed the embargo on the study abstract had been breached and lifted the embargo on the full dataset Thursday afternoon, and trading was briefly paused for volatility. Analysts quoted in the coverage called the reversal a sell-the-news reaction after a months-long surge in which the stock had risen more than 500% this year and had nearly quadrupled through Wednesday's close since the August success announcement.

Expectations explain the rest. Before the meeting, investors were looking for a recurrence-risk cut of 40% or more, and the delivered 42% cleared that bar only narrowly. The Phase 3 recurrence hazard ratio of 0.58 was also a smaller relative benefit than the earlier Phase 2b trial's hazard ratio of 0.51 after roughly five years, the mid-stage figure investors had anchored on. One analyst described the recurrence data as solid and the pullback as an expected sell-the-news event, while another described the data as great and said investors may now question whether the treatment will prove as effective in other cancer types to justify the high valuation.

What remains unproven

Nothing in Thursday's release proves a survival benefit, an approval, or revenue. Overall survival is a favorable trend on immature data, not a demonstrated endpoint, and the regulatory path is described only as engagement with authorities. The broader test is the INTerpath program itself, which the companies count at nine Phase 2 and Phase 3 trials across tumor types, including three ongoing Phase 3 trials in non-small cell lung cancer, building on the Phase 2b five-year follow-up presented earlier this year. What to watch next is the full presentation in Madrid on Saturday, any regulatory filing that follows the engagement the companies described, the maturing overall survival data, and whether the after-six-months benefit pattern holds as follow-up lengthens beyond the current median of 24.6 months.