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 $22.6 billion (as of July 23, 2026) — a fraction of what it could be if the cancer vaccine platform works.

What we’re watching

1. The detailed data presentation. The hazard ratio for RFS has not been released — the companies will present it at an upcoming medical meeting. This number determines whether analysts model $2 billion or $5 billion in peak sales.
2. INTerpath-002 kidney cancer readout. Expected late 2026 or early 2027. A win here doubles the addressable market and validates the platform beyond melanoma.
3. Regulatory filing. The companies plan to begin discussions with regulators “in the next few months,” targeting a BLA submission and potential accelerated approval. The earlier “November 15 PDUFA” framing is now superseded.
4. Expansion trials. NSCLC, renal cell carcinoma, and head and neck cancer Phase 2 data continue to mature.

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

Update August 21, 2026 (MAJOR): The Phase 3 readout happened — and it hit. On August 19, Moderna and Merck announced the Phase 3 INTerpath-001 trial met its primary endpoint of recurrence-free survival (and the key secondary endpoint of distant metastasis-free survival) at a pre-planned interim analysis. MRNA closed at $174.38 on August 19, up 177% from $62.96, then pulled back about 20% to close at $133.32 on August 20 (Polygon). This supersedes the “wait for Phase 3” bear case below — the binary catalyst resolved positive. The companies plan to begin regulatory discussions “in the next few months,” so the November 15 PDUFA and November 7 AdCom dates cited below are no longer the operative timeline. See our breaking coverage: Moderna Surges 177% as Intismeran Clears Phase 3 Melanoma Trial.

Last updated July 31, 2026: Moderna reported Q2 2026 earnings on July 31: revenue of $145 million (beating analyst estimates of $106.7 million by 35.8%), GAAP EPS of -$1.97 (beating by $0.09). Despite the beat, shares fell approximately 6% as the market focused on continued cash burn and the gap between current revenue and the market cap. The company reiterated its target of up to 10% revenue growth for 2026 and expects approximately 55% of H2 2026 revenue in the second half. The August 5 PDUFA for mRNA-1010 (flu vaccine) is the next near-term catalyst, with the November 15 PDUFA for mRNA-4157 (cancer vaccine) further out. MRNA closed at $54.82 on July 31, down 5.4% from the $57.92 July 30 close and down 19.7% from the $68.28 July 16 publication price. Market cap is approximately $21.8 billion.

Update August 9, 2026: mFLUSIVA (mRNA-1010) was approved by the FDA on August 5 — the first mRNA-based seasonal influenza vaccine in the US. MRNA closed at $59.17 on August 7 (Polygon), recovering from the $54.82 July 31 post-earnings low and up 3.9% from the original $57.02 article reference price. The approval does not change the mRNA-4157 thesis — the cancer vaccine PDUFA (November 15) and INTerpath Phase 3 remain the key catalysts. See our mFLUSIVA approval coverage.