Healthcare’s Best Week Since June Traces Back to a Single Moderna and Merck Cancer Trial

The health-care sector was on track for its strongest week since June 26, with the Health Care index rising more than 4% in the five trading days leading up to August 21, compared to a 7.9% increase in late June. The spark was a single piece of clinical trial news: Moderna Inc. (NASDAQ: MRNA ) and Merck & Co., Inc. (NYSE: MRK ) announced on August 19 that their tailored mRNA cancer treatment was successful in a late-stage trial, significantly improving recurrence-free survival and distant metastasis-free survival compared with Keytruda alone in a study of over 1,100 patients.

The Phase 3 trial, dubbed INTerpath-001, tested an individualized cancer vaccine called intismeran autogene in combination with Merck's blockbuster immunotherapy Keytruda in patients with completely resected stage IIB-IV melanoma, meaning their visible cancer had already been surgically removed and the treatment was meant to prevent it from returning.

The trial achieved both its primary goals, recurrence-free survival, and a critical secondary target, distant metastasis-free survival, when compared to Keytruda alone. The companies stated that no new safety signals arose throughout the trial, and that the results expanded on previous Phase 2b data showing that the combination reduced the risk of recurrence or death by 49% and the risk of distant metastasis or death by 59% compared to Keytruda alone.

Why Researchers Are Calling It a Landmark

The results are significant beyond melanoma. Personalized "neoantigen" vaccines have been considered as a cancer treatment concept for many years, but this is the first randomized Phase 3 experiment to definitely confirm their effectiveness. Dr. Julie Gralow, chief medical officer of the American Society of Clinical Oncology, described the results as a monumental step forward in validating mRNA technology as a cancer treatment, while Moderna Inc. (NASDAQ:MRNA) CEO Stéphane Bancel told CNN that the results were comparable in significance to the company's November 2020 COVID-19 vaccine data, describing the event as a new chapter in cancer care.

Even by biotech standards, the market reacted strongly to the study results. Moderna Inc. (NASDAQ:MRNA) shares rose around 177% on the day of the news, adding approximately $45 billion to the company's market capitalization, showing how low expectations for Moderna had gotten. Shares that had formerly traded above $400 had slipped below $30 for much of 2025, owing to slowing vaccine sales and the lack of a clear future blockbuster product. Merck & Co., Inc. (NYSE:MRK) posted a more modest but still significant 12% single-day rise.