Merck-Moderna Cancer Vaccine Combination Meets Two Phase 3 Melanoma Endpoints

Merck and Moderna said their individualized mRNA cancer therapy combined with Keytruda met both the primary and a key secondary efficacy endpoint in a Phase 3 melanoma trial, giving the partners their first positive late-stage readout for the program. The INTerpath-001 study showed statistically significant and clinically meaningful improvements in recurrence-free survival and distant metastasis-free survival compared with Keytruda alone in patients whose stage IIB through IV cutaneous melanoma had been completely removed by surgery.

The companies disclosed topline findings from a prespecified interim analysis but did not release the Phase 3 hazard ratios, confidence intervals, event counts or p-values. That means the announcement establishes that the study crossed its statistical thresholds for the two reported endpoints, but the size and durability of the benefit cannot yet be independently assessed from the public data.

Merck and Moderna said in their August 19 announcement that the trial will continue to evaluate other key secondary endpoints, including overall survival. They plan to present detailed results at an upcoming international medical meeting and engage regulators on potential filing submissions for intismeran autogene, also known as V940 or mRNA-4157, in combination with Keytruda.

Topline result clears two efficacy measures, with overall survival still pending

Recurrence-free survival was the primary endpoint in INTerpath-001. It measures the time from randomization until melanoma returns or the patient dies from any cause. Distant metastasis-free survival, one of the trial’s key secondary endpoints, measures whether cancer spreads to distant parts of the body or the patient dies. Both measures are especially relevant in the adjuvant setting, where treatment is given after surgery to lower the risk that disease will return.

The companies said the combination produced statistically significant and clinically meaningful improvements in both measures versus Keytruda alone. They also said the safety profiles of intismeran and Keytruda were consistent with what had been observed in earlier studies of the combination, with no new safety signals identified in this analysis.

What is not yet public is equally important. Merck and Moderna have not disclosed a numerical estimate of the Phase 3 reduction in the risk of recurrence, distant metastasis or death. They have also not reported overall-survival results from the trial. The study is continuing under its protocol to assess that endpoint and other secondary measures, including safety, tolerability and quality of life.

The companies described INTerpath-001 as the first positive Phase 3 readout for an individualized neoantigen therapy and for an mRNA-based cancer therapy. That characterization comes from Merck and Moderna and will be easier to evaluate once the full dataset is presented. The immediate development milestone is nevertheless clear: the program has moved from encouraging randomized Phase 2 evidence to a Phase 3 trial that met its prespecified primary efficacy test.

Phase 3 trial adds a patient-specific mRNA therapy to Keytruda

INTerpath-001 enrolled 1,137 patients with completely resected stage IIB, IIC, III or IV cutaneous melanoma who had not previously received systemic therapy. According to the companies and the ClinicalTrials.gov study record, the global trial is randomized, double-blind and controlled with both placebo and an active comparator.

Patients were randomized 2:1 after surgery. The experimental group received intismeran at 1 milligram every three weeks for as many as nine doses plus Keytruda at 400 milligrams every six weeks for as many as nine cycles. The control group received Keytruda alone. Treatment could continue for about a year, with a maximum duration of roughly 56 weeks, unless disease recurred or toxicity required treatment to stop sooner.

Intismeran is not an off-the-shelf vaccine made identically for every patient. The therapy is designed from an individual patient’s tumor sample. Merck and Moderna use the tumor’s mutational profile to select neoantigens, which are abnormal proteins associated with the cancer, and produce a synthetic mRNA treatment encoding as many as 34 of them. The aim is to train the immune system to recognize tumor-specific targets and generate T-cell responses against cancer cells.

Keytruda, or pembrolizumab, works through a different mechanism. It is an anti-PD-1 therapy that blocks an immune checkpoint cancer cells can use to avoid immune detection. Keytruda is already approved in the United States as adjuvant treatment after complete resection for certain patients with stage IIB, IIC or III melanoma, as well as for unresectable or metastatic melanoma. INTerpath-001 is therefore testing whether a personalized mRNA therapy can improve outcomes when added to an established immunotherapy rather than replacing it.

That distinction also helps explain why the partners’ result matters commercially as well as scientifically. If regulators eventually approve the combination, intismeran would add a patient-specific manufacturing and treatment component to a Keytruda-based regimen. The companies have not yet disclosed a proposed price, filing timetable or commercial launch schedule, and the candidate remains investigational.

Five-year Phase 2 data and a decade-long partnership preceded the Phase 3 readout

The Phase 3 result builds on the smaller KEYNOTE-942 Phase 2b study, which enrolled 157 patients with high-risk stage III or IV melanoma after complete resection. At a planned five-year follow-up presented in 2026, the combination was associated with a 49% reduction in the risk of recurrence or death compared with Keytruda alone, with a hazard ratio of 0.51 and a 95% confidence interval of 0.294 to 0.887.

The same Phase 2b follow-up showed a 59% reduction in the risk of distant metastasis or death, with a hazard ratio of 0.411 and a 95% confidence interval of 0.200 to 0.843. Those figures should not be assumed to match the Phase 3 effect size because the new study is larger, has a different population that includes stage IIB disease and has not yet disclosed its numerical efficacy results.

The regulatory path has also been developing for several years. The U.S. Food and Drug Administration granted the combination Breakthrough Therapy Designation in February 2023 for adjuvant treatment of high-risk melanoma after complete resection, based on the Phase 2b findings. That designation is intended to facilitate development and review when preliminary clinical evidence indicates that a treatment for a serious condition may offer a substantial improvement over available therapy, but it is not an approval.

Merck and Moderna’s cancer-vaccine collaboration dates to 2016 and was amended in 2018. In October 2022, Merck paid Moderna $250 million to exercise an option to jointly develop and commercialize personalized cancer vaccines including V940. Under that worldwide collaboration, the companies agreed to share development costs and any profits equally.

The partnership has since expanded intismeran into a broader clinical program. Merck and Moderna said the INTerpath program now includes nine Phase 2 and Phase 3 trials across melanoma, non-small cell lung cancer, bladder cancer and renal cell carcinoma, alongside other clinical work. That makes the melanoma result more than a single-trial event: it is the first Phase 3 efficacy test to report out from a platform the companies are evaluating across multiple tumor types and stages of disease.

For the melanoma program, the next major information gap is the detailed Phase 3 dataset. The magnitude of the RFS and DMFS benefit, the maturity of the data, subgroup results and longer-term safety will matter for judging how the combination compares with Keytruda alone. Overall survival remains under evaluation. Merck and Moderna’s stated next steps are to present the data at an international medical meeting and discuss filing submissions with regulatory authorities.