Merck, Moderna unveil phase 3 trial details for closely watched mRNA cancer vaccine

After a major phase 2 win that stirred up much excitement within the oncology community, Merck & Co. has officially formulated a pivotal trial plan for its Moderna-partnered personalized cancer vaccine, mRNA-4157.

A phase 3 trial coded V940-001 will test the combination of the mRNA vaccine, also known as V940, and Merck’s PD-1 inhibitor Keytruda for post-surgery treatment of patients with resected melanoma that’s at high risk of recurrence. The trial was posted on Thursday and is expected to kick off Aug. 1.

The vaccine is made by profiling each patient’s tumor mutational signature and is designed to induce an immune response against the corresponding antigens. If eventually successful, Merck and Moderna could open up an entirely new area of cancer treatment.

Merck pushed V940 into phase 3 after the phase 2b KEYNOTE-942 study showed that the vaccine’s combination with Keytruda reduced the risk of recurrence or death by 44% compared with Keytruda alone for the adjuvant, or post-surgery, treatment of resectable melanoma. 

Both studies use Keytruda monotherapy as the comparator and use recurrence-free survival as the primary endpoint. But the phase 3 trial is different from its predecessor in several ways.

First, while the midstage trial data included patients with stage 3b to 4 melanoma, the new phase 3 stretches to disease as early as stage 2b.

The wider patient population didn’t come as a surprise, Leerink Partners analyst Daina Graybosch, Ph.D., said in an email with Fierce Biotech. Keytruda monotherapy is currently approved as an adjuvant treatment for stage 2b to 3 melanoma following complete resection, and Merck has said it plans to cover the entire spectrum where Keytruda is approved, she noted.

V940-001 is expected to enroll 1,089 patients, making it much larger than the 157-patient phase 2b study. The ongoing midstage trial started mid-2019 and read out positively toward the end of 2022. By comparison, V940-001 bears a primary completion date six years from now in October 2029. It’s not clear what plan Merck has for any interim analyses. A spokesperson said the company will share more information once the trial has been initiated.

If we look for past experience, Bristol Myers Squibb previously found that adding its CTLA-4 agent Yervoy to the adjuvant Opdivo didn’t improve recurrence-free survival in stage 3b to 4 melanoma. The company announced the failure of CheckMate-915 in October 2020, three and a half years into the study.

PD-1 inhibitors are the current standard of care in adjuvant melanoma, so Keytruda is the appropriate comparator for V940-001. But by the time the trial reads out, a new standard of care could have emerged, Graybosch noted.

BMS is nearly two years into the RELATIVITY-098 trial for its PD-1/LAG-3 combo Opdualag in stage 3 to 4 melanoma, with primary completion data estimated for February 2026. Merck itself recently launched another phase 3 trial dubbed KEYVIBE-010, which is pairing Keytruda with the TIGIT inhibitor vibostolimab.

Compared with the new cancer vaccine study, that TIGIT trial is larger with a planned 1,560 participants and has an earlier primary completion date in October 2027. Both trials are in stage 2 to 4 melanoma.

The smaller trial size for V940-001 could reflect Merck’s confidence in the cancer vaccine’s efficacy given the strong phase 2b results. But the longer trial timeline could mean that the company expects more follow-up time to see a clear efficacy signal for the vaccine.

Cancer vaccines have seen many failures in the past, and the encouraging phase 2b KEYNOTE-942 results gave people hope that the personalized mRNA vaccine might end the category’s troubled history.

Graybosch expects that any statistically significant data from V940-001 could change practice, “especially as the vaccine is so tolerable.”