Moderna Plunges 25% on Apparent Leak of Melanoma Vaccine Data

Moderna (MRNA) shares plunged about 25% on Thursday, on pace for their largest decline since the company went public, according to the summary supplied, after detailed Phase 3 results for its personalized melanoma vaccine with Merck (MRK) apparently leaked online ahead of their scheduled presentation. The results appeared on the Oncology Central website at about 12:30 p.m. ET and were taken down soon afterward, according to Investing.com. The leaked figures suggest the vaccine plus Keytruda cut the risk of melanoma recurrence or death by 42%, less than the 49% reduction seen in the earlier Phase 2b trial. Moderna declined to comment. Full results are due at the ESMO Congress in Madrid on Saturday, Oct. 24.

What leaked

The trial, INTerpath-001, tested the individualized neoantigen therapy intismeran autogene plus Merck's Keytruda against Keytruda alone in 1,137 patients with resected high-risk (stage IIB to IV) melanoma. According to Investing.com, the leaked data show the combination reduced the risk of recurrence or death by 42%, with 82.2% of patients in the combination arm alive and cancer-free after two years versus 70% on Keytruda alone. The summary supplied cited a hazard ratio of 0.58, which by our calculation matches a 42% risk reduction. Neither Moderna nor Merck has confirmed the leaked figures.

In August, Moderna and Merck said the Phase 3 trial met its primary endpoint of recurrence-free survival and its key secondary endpoint of distant metastasis-free survival, calling the results statistically significant and clinically meaningful, without releasing numbers. Merck said at the time that the safety profile was consistent with earlier studies, with no new safety signals.

Market reaction

Moderna traded around $185 in the afternoon, according to 24/7 Wall St. and Investing.com, after the stock hit a 52-week high of $254.48 the prior session and was up more than 500% for the year. Investing.com reported a volatility halt in the shares during the session. Merck was down about 1%, and the summary supplied put the decline at 1.5%. BioNTech (BNTX), which has its own individualized mRNA cancer candidate, fell about 2%. The S&P 500 was down roughly 1.3%.

The summary supplied said the findings raised questions about whether the vaccine adds enough benefit over existing immunotherapy to justify its potential cost, especially after the stock's rally. Citi's Geoff Meacham maintained a Sell rating with an $80 price target, and TD Cowen raised its target to $90 from $40 with a Hold rating, according to Investing.com.

What comes next

Georgina Long is scheduled to present the Phase 3 data in the ESMO Presidential Symposium on Saturday, Oct. 24, at 10:30 a.m. ET. Moderna will host an investor webcast the same day at 1:00 p.m. ET on its investor relations site. The hazard ratios, confidence intervals and overall survival and safety data are expected then.

Sources: Merck and Moderna Phase 3 INTerpath-001 announcement (Aug. 19) and Moderna's ESMO 2026 announcement (Sept. 21); Investing.com and 24/7 Wall St. (Oct. 22). Leaked figures are unconfirmed by the companies; Thursday's stock moves are as reported and in the summary supplied. This is informational, not a recommendation to buy or sell.