Moderna's mRNA-4157 Cancer Vaccine: Phase 2 Data Shows 44% RFS Reduction in Melanoma

Moderna’s mRNA-4157 — the personalized cancer vaccine paired with Merck’s Keytruda — is the most-watched mRNA program outside of infectious disease. And for good reason.

The concept

mRNA-4157 is a custom-made vaccine. For each patient, doctors sequence the patient’s tumor, identify up to 34 neoantigens (mutations unique to that tumor), and Moderna designs an mRNA vaccine that teaches the immune system to attack those specific mutations.

It’s the ultimate in personalized medicine: a vaccine made for one person, targeting one tumor. If it works, the implications are enormous.

The data

The Phase 2b trial enrolled 157 patients with high-risk melanoma (Stage III/IV, fully resected). All patients received Keytruda; half also received mRNA-4157.

The results:

• Recurrence-free survival (RFS): 44% reduction in risk of recurrence or death vs. Keytruda alone (p = 0.026)
• Distant metastasis-free survival (DMFS): 41% reduction in risk of distant metastasis or death (p = 0.034)
• 24-month RFS rate: 79% (combo) vs. 67% (Keytruda alone)

The data was enough for FDA Breakthrough Therapy designation and started Phase 3. The Phase 3 trial is enrolling 600+ patients across multiple melanoma subtypes.

The PDUFA

An November 15 PDUFA date could make mRNA-4157 the first-ever approved mRNA cancer vaccine. But the FDA may wait for Phase 3 data — the Phase 2b trial was small (157 patients), and the FDA typically requires confirmatory data for accelerated approval.

The bull case: the FDA grants accelerated approval based on Phase 2b RFS data, and Moderna launches while Phase 3 runs. This would be a paradigm-shifting event.

The bear case: the FDA waits for Phase 3, which reads out in 2027-2028. Moderna’s stock treads water until then.

The market

Melanoma is just the beginning. Moderna and Merck are running Phase 2 trials in non-small cell lung cancer (NSCLC), renal cell carcinoma, and head and neck cancer. If the platform works in melanoma, it could work across solid tumors.

Peak sales estimates range from $5–15 billion across indications. Moderna’s market cap is currently $25 billion — a fraction of what it could be if the cancer vaccine platform works.

What we’re watching

1. November 15 PDUFA: Accelerated approval vs. wait for Phase 3. This is the binary event.
2. November 7 AdCom: The VRBPAC will review the personalized vaccine manufacturing process. If the committee raises concerns about consistency, it’s a red flag.
3. Phase 3 interim data: Could read out in late 2027. Early signals on efficacy will move the stock.
4. Expansion trials: NSCLC Phase 2 data is expected in 2027. If positive, it validates the platform beyond melanoma.

mRNA-4157 is the reason Moderna’s stock has been resilient post-COVID. The cancer vaccine platform is the future of the company.