Shares of Merck & Co., Inc. (NYSE: MRK) slipped 0.67% to $148.87, down $1.01, as midday selling erased earlier gains, even as the company and Moderna reported positive Phase 3 results for a personalized melanoma therapy the two drugmakers developed together. The companies said patients who received the experimental mRNA treatment alongside Merck's immunotherapy KEYTRUDA showed lower risks of cancer recurrence and distant spread.

Phase 3 Trial Shows Lower Melanoma Recurrence Risk

The investigational therapy, intismeran autogene (also known as mRNA-4157/V940), is tailored to the genetic changes found in each patient's tumor. Built on Moderna's mRNA platform, it is designed to help the immune system recognize cancer-related targets. Melanoma, the most serious form of skin cancer, can recur even after surgical removal, making effective post-surgery treatment a priority for patients with advanced-stage disease. Researchers tested the therapy in combination with KEYTRUDA, Merck's anti-PD-1 immunotherapy, in patients who had undergone surgery for melanoma.

The INTerpath-001 trial enrolled 1,137 patients with completely resected stage IIB through IV melanoma. Participants were assigned to receive either intismeran plus KEYTRUDA or placebo plus KEYTRUDA. After a median follow-up of 24.6 months, the combination had reduced the risk of recurrence or death by 42%.

The regimen also cut the risk of distant metastasis or death by 38% compared with KEYTRUDA alone. Both findings met statistical significance, and researchers observed broadly consistent benefits across planned patient subgroups. Overall survival data remain immature, although the companies reported a favorable trend for the combination.

Two-Year Results Detail Benefits and Side Effects

At the two-year mark, 82.2% of patients in the combination arm remained free from recurrence, compared with 70.0% of those receiving KEYTRUDA alone. The corresponding rates for remaining free from distant metastasis were 88.5% and 80.2%. Neither treatment group had reached its median recurrence-free or distant metastasis-free survival point.

During the first six months, researchers found similar recurrence and distant metastasis outcomes across the two groups. A planned six-month analysis, however, showed a 58% lower risk of recurrence or death with the combination, along with a 50% lower risk of distant metastasis or death. The six-month figures and the longer-term estimates reflect different follow-up windows within the same study, so the two sets of numbers describe the treatment effect at separate points in time.

Treatment-related side effects affected 95.8% of combination recipients and 90.0% of the comparison group. Grade 3–5 treatment-related events occurred in 14.2% and 13.4% of patients, respectively. Fever, injection-site pain, and fatigue were the most commonly reported reactions among patients who received the combination.

Merck and Moderna Pursue Broader Cancer Studies

Merck and Moderna plan to discuss the trial findings with regulators as they continue collecting survival data. The companies also intend to present detailed results at the 2026 European Society for Medical Oncology Congress, and the New England Journal of Medicine has accepted the findings for publication. Those steps—the regulator discussions, the maturing survival dataset, the congress presentation, and the journal publication—make up the program's most concrete near-term milestones.

The partners are running nine Phase 2 and Phase 3 studies across several cancer types and disease stages. Three of the Phase 3 trials focus on non-small cell lung cancer, while other studies examine additional treatment settings. Researchers are also evaluating intismeran in pancreatic and gastric cancers. How the combination performs in those settings remains to be established by the ongoing trials.

Earlier Phase 2b melanoma results supported the companies' decision to advance the personalized treatment into larger trials, though the latest study has not yet established a final overall survival benefit. Merck shares nonetheless finished lower despite the reported clinical progress and the continued development plans.

Source: Blockonomi