Intismeran: The First mRNA Cancer Vaccine That Wor
1,137 Patients. Two Endpoints. The First mRNA Cancer Vaccine That Actually Works.
On August 19 2026, Moderna and Merck announced that the Phase 3 INTerpath-001 trial of intismeran autogene had met both its primary endpoint of recurrence-free survival and its key secondary endpoint of distant metastasis-free survival in patients with high-risk resected melanoma. No mRNA-based cancer therapy had ever done that before. No individualised neoantigen therapy of any kind had ever done that before. This was the result the field had spent a decade building toward.
What Intismeran Actually Is
Intismeran is not a conventional cancer drug. It is built from a biopsy of your own tumour. Scientists sequence your DNA, identify mutations that are unique to your cancer, and encode up to 34 of those targets into a custom mRNA strand. Injected into your arm, it trains your immune system to recognise and hunt cells carrying those exact mutations. No two patients receive the same vaccine. The drug is given alongside Keytruda (pembrolizumab), Merck's immunotherapy that is already a standard of care in melanoma. In INTerpath-001, 1,137 patients were randomised 2:1: either intismeran plus Keytruda, or Keytruda alone for roughly a year after surgery. All had stage IIB to IV melanoma that had been fully removed but carried a high risk of returning.
Patients enrolled in INTerpath-001 (Phase 3)
1,137
Endpoints met
Recurrence-free survival (RFS) and distant metastasis-free survival (DMFS)
Recurrence risk reduction in Phase 2b (KEYNOTE-942, 157 patients)
49% lower vs Keytruda alone (HR=0.51)
Distant metastasis risk reduction in Phase 2b
59% lower vs Keytruda alone (HR=0.41)
FDA Breakthrough Therapy Designation
Granted 2023 based on Phase 2b data
New melanoma cases diagnosed worldwide per year
330,000 (2022 figure)
Projected new US melanoma cases in 2026
112,000
Why the Phase 2b Numbers Matter So Much
The Phase 3 trial has confirmed that the drug works but has not yet released its hazard ratios. The numbers everyone is anchoring against come from Phase 2b (KEYNOTE-942), presented at the 2026 ASCO Annual Meeting as five-year follow-up data. In that trial, 157 patients with stage IIIB to IV melanoma received intismeran plus Keytruda or Keytruda alone. At 60 months median follow-up, the combination showed a 49% reduction in the risk of recurrence or death (HR=0.51) and a 59% reduction in the risk of distant metastasis or death (HR=0.41). An exploratory analysis found a survival trend favouring the combination (HR=0.47), though the sample was too small to be conclusive. No new safety signals emerged across five years. What this means: patients who had already had their melanoma surgically removed, and who were already receiving one of the best immunotherapies available, did meaningfully better when intismeran was added. The Phase 3 trial, with seven times as many patients, confirmed th
"This is the first Phase 3 study to show that intismeran, given in combination with pembrolizumab, can reduce the risk of recurrence.
"Professor Georgina Long
"These first Phase 3 findings reinforce the promise of a more personalised approach to cancer treatment.
"Dr. Dean Y. Li
The Stock Story Is Also a Science Story
The market's reaction tells you something about how long and how sceptically the investment world had been waiting for this. Moderna's share price closed at $62.96 on August 18. The day after the INTerpath-001 announcement it closed at $174.38: a 177% single-day gain, the largest in the company's history. Market capitalisation moved from roughly $25 billion to $69 billion. Short sellers, who held 13.37% of freely traded shares, lost an estimated $4.8 billion as the price forced them to buy back. After a 20% pullback the following day, shares settled near $145. That is still more than twice the pre-announcement close. Context matters here too. Before the cancer announcement Moderna was already up 357% in 2026, driven by the FDA approval of mFlusiva, the first mRNA flu vaccine. The stock had collapsed 95% from its COVID-era peak of $484 to $22 before that recovery began. The INTerpath-001 result added a second story on top of a building that was already being rebuilt.
What Comes Next
Merck and Moderna plan to present full INTerpath-001 data at the ESMO Congress in Madrid on October 23 to 27 2026. The hazard ratios, confidence intervals, subgroup analyses and overall-survival data are not yet public. Analysts at JPMorgan had already assigned an 85% probability of success before the readout; the actual number now heading into ESMO is 100%. The companies have said they will begin regulatory filing discussions immediately. Phase 3 in a second cancer is already underway. INTerpath-002 is evaluating intismeran plus Keytruda in resected non-small-cell lung cancer (stages IB to IIIA), with a first readout expected in late 2026 or 2027. Lung cancer kills roughly 1.8 million people per year, making it a far larger target than melanoma. If INTerpath-002 reads out positive, the total addressable market for intismeran expands by an order of magnitude.
