Merck-Moderna cancer vaccine win spurs stock jump, speculation of Keytruda-like impact

Biotech Merck-Moderna cancer vaccine win spurs stock jump, speculation of Keytruda-like impact By Nick Paul Taylor Aug 20, 2026 9:25am Merck & Co. Moderna cancer vaccine Keytruda As the dust settles on a phase 3 announcement that added $45 billion to Moderna’s market cap, analysts have begun to ask a question that could define cancer care in the coming years: can use of the vaccine be as broad as Keytruda? Moderna’s share price closed up 177% on Wednesday following the disclosure of a topline win from a phase 3 trial of its Merck & Co.-partnered cancer vaccine.

Analysts at Evercore ISI and William Blair cited the involvement of retail investors and short sellers, respectively, as factors in the surge—but that only partly explains the jump. Shares in Merck, which has a much larger market cap, closed up almost 13%. The stock increases reflect the potential for the cancer vaccine, intismeran autogene, to work in settings beyond the adjuvant melanoma indication covered by Wednesday’s INTerpath-001 update.

Sales in adjuvant melanoma could exceed $2 billion, Guggenheim Securities analysts said, but broader use will be needed to justify Moderna and Merck’s newly inflated valuations. As William Blair analysts noted, the debate among investors “will now turn to how much the INTerpath-001 data have de-risked intismeran in other cancer settings and if this product can be as broad as Keytruda.” Merck grew annual Keytruda sales to north of $30 billion by validating the checkpoint inhibitor in a long list of indications. Last month, David Berman, M.D., Ph.D., chief development officer at Moderna, told investors there is “increased reason to believe” that intismeran will work against diseases vulnerable to Keytruda.

The “big question,” Berman said at the time, is whether intismeran works outside those settings. Analysts have generated towering sales estimates even without factoring in the potential for intismeran to work in settings where checkpoint inhibitors have struggled, such as pancreatic cancer. Based on the phase 3 success, William Blair analysts predicted Moderna could book $5.4 billion in intismeran sales in melanoma by 2040 under its 50-50 profit-share agreement with Merck.

The analysts’ Moderna model for 2040 now includes sales of $10 billion in non-small cell lung cancer (NSCLC) and sales of $3.3 billion in renal cell carcinoma (RCC). In RCC, the analysts see “upside potential ... pending more effective therapies in this high-unmet-need indication.” Merck and Moderna are running nine phase 2 and 3 trials, providing opportunities beyond melanoma, NSCLC and RCC.

For Moderna, the studies represent a chance to diversify beyond its flatlining COVID-19 vaccine business. The trials are key to Merck too, with Guggenheim analysts noting that intismeran could be an important part of the drugmaker’s growth “as it works to navigate through biosimilar and pricing pressure for Keytruda starting later this decade.” Keytruda could face biosimilar competition in 2028. The next question is whether the excitement survives a look at the full data from the adjuvant melanoma trial.

Merck and Moderna need a hazard ratio of 0.65 or lower to clearly differentiate intismeran, William Blair analysts said. A hazard ratio above 0.75 would underwhelm the analysts, who cautioned that the share price moves price in “substantially more conviction than the data disclosed thus far supports.” Multiple companies could be hit by the fallout if the phase 3 numbers underwhelm. The share prices of Arcturus Therapeutics and BioNTech closed up more than 20% on Wednesday.

Guggenheim analysts noted the potential for intismeran to drive interest in Arcturus’ platform, while the TD Cowen team framed the Merck-Moderna readout as a “positive signal” for BioNTech’s cancer vaccine. Merck & Co. Moderna cancer vaccine Keytruda mRNA immuno-oncology melanoma Biotech