Merck and Moderna report first positive late-stage trial results for personalized mRNA melanoma vaccine

Phase 3 trial findings

Merck and Moderna announced on 19 August 2026 that their personalized mRNA cancer vaccine combined with immunotherapy met its primary and secondary endpoints in a late-stage clinical trial. The study represents the first positive Phase 3 trial outcome reported for an mRNA-based cancer therapy. Conducted under the trial name INTerpath-001, the study evaluated high-risk patients with stage IIB, stage IIC, stage III, or stage IV melanoma whose tumors had previously been surgically removed. A total of 1,137 patients were randomized to receive either Merck's immunotherapy drug Keytruda alone or Keytruda in combination with up to nine doses of the individualized vaccine for approximately one year. The companies confirmed statistically significant improvements in recurrence-free survival and confirmed that the treatment met its secondary target of preventing cancer cells from spreading to distant organs. No new safety signals emerged during the ongoing trial period.

Professor Georgina Long, the study principal investigator and medical director of Melanoma Institute Australia, commented on the clinical significance of the findings.

Today's results represent a landmark moment for adjuvant melanoma treatment.

Mechanism and customized design

The experimental drug, known as Intismeran autogene, V940, or mRNA-4157, uses synthetic messenger RNA to direct cells to produce proteins that trigger an immune response against tumors. Unlike traditional vaccines intended to prevent infection before exposure, Intismeran serves as a therapeutic post-surgical intervention. Moderna manufactures each treatment individually by analyzing the specific genetic mutations present in a patient's surgically excised tumor tissue. The custom mRNA instructions train and stimulate the patient's immune system to identify and attack up to 34 distinct mutation targets on recurring cancer cells. Combining this personalized formulation with Keytruda aims to strengthen the body's overall anti-tumor defenses.

Stéphane Bancel, the chief executive officer of Moderna, reflected on the development of individualized genetic therapies.

For many years, the idea of creating an mRNA treatment designed specifically for an individual's cancer was hard to imagine. Today, we are helping to transform that vision into reality.

Clinical progression and regulatory path

The Phase 3 milestone follows years of clinical development by both pharmaceutical partners. In January 2026, Merck and Moderna announced results from a mid-stage trial showing that the combination treatment reduced the risk of melanoma recurrence or death by 49% after five years. The positive Phase 3 results arrive after the United States Food and Drug Administration rejected an earlier application by Moderna for accelerated approval in 2024. While detailed statistical percentages were not released in the initial announcement, the companies stated that they will present full data at an upcoming medical conference. The drugmakers also plan to submit the complete clinical trial dossier to regulatory authorities to seek formal market authorization.

Market reaction and oncology pipeline

Following the announcement, shares of both companies climbed in pre-market trading on the Nasdaq and Wall Street. Moderna shares gained across pre-market sessions, rising between 10% and nearly 100% to touch intraday highs near $110, while Merck shares advanced between 2% and 8% to reach $146. JPMorgan analysts previously identified Intismeran as the central product in Moderna's pipeline to support its commercial transition from respiratory vaccines toward oncology treatments. Moderna established its initial public profile during the coronavirus pandemic through its COVID-19 vaccine, but changing market demand has shifted focus toward individualized cancer applications. The mRNA platform is currently being evaluated across nine active clinical trials targeting diverse cancer indications and disease stages. Melanoma remains the deadliest form of skin cancer, with National Cancer Institute records showing over 1.5 million people in the United States living with the condition in 2023.