Merck announced its personalised cancer vaccine combined with immunotherapy Keytruda significantly improved outcomes for melanoma patients in a Phase 3 trial. The 135-year-old drugmaker's stock jumped 12.6% on 19 August following the news. The trial tested intismeran autogene, developed with Moderna, alongside Keytruda in patients with surgically removed stage IIB through IV melanoma. Patients receiving the combination stayed cancer-free longer and experienced delayed cancer spread compared to those on Keytruda alone. The treatment uses mRNA technology tailored to each patient's tumour mutations, training the immune system to target up to 34 specific genetic changes. It marks the first time an individualised cancer vaccine has shown positive results in late-stage testing. Keytruda generated $8.4 billion in second-quarter sales, representing over 50% of Merck's quarterly revenue.

Moderna shares fell 13% in premarket trading Thursday as investors took profits after the biotech company's historic rally. The stock had more than doubled on 19 August following successful Phase 3 results for its personalised mRNA cancer vaccine, developed with Merck. The trial involving over 1,100 melanoma patients met its primary and key secondary endpoints, marking the first successful large-scale late-stage cancer trial for an mRNA therapy. Fresh analyst targets added to valuation concerns. RBC Capital raised its price target to $130 but kept a Sector Perform rating. Bank of America upgraded shares with a $170 target. Both remained below Wednesday's close of $174.38. Moderna reported a $782 million net loss in Q2 2026 and negative operating cash flow.

Elon Musk endorsed mRNA technology on Wednesday, describing it as having "tremendous promise" and likening disease treatment to a "software problem" through artificial RNA. His comments followed a major cancer vaccine breakthrough by Moderna and Merck. The companies announced positive Phase 3 results for an individualised mRNA cancer vaccine — the first successful late-stage trial of its kind. The treatment showed significant improvement in recurrence-free and metastasis-free survival in melanoma patients when combined with Merck's Keytruda. Musk was responding to scientist Eric Topol, who highlighted the trial's success alongside progress in personalised mRNA vaccines for pancreatic cancer, triple-negative breast cancer, and non-small cell lung cancer. Moderna shares surged 177%, whilst BioNTech gained 21.96% and Arcturus Therapeutics rose 25.21%. Musk has previously promoted AI and synthetic RNA as paths to transforming healthcare.