Why Is Regeneron Stock Sinking Monday?

by | May 18, 2026 | General

On Friday, Regeneron Pharmaceuticals, Inc. (NASDAQ:REGN) reviewed results from the Phase 3 trial evaluating two dose levels of fianlimab (LAG-3 inhibitor) in combination with Libtayo (cemiplimab) for unresectable locally advanced or metastatic melanoma.

Phase 3 Melanoma Trial Misses Primary Endpoint

The trial did not reach statistical significance for the primary endpoint of improvement in progression-free survival (PFS) compared to Merck & Co. Inc. (NYSE:MRK) Keytruda (pembrolizumab) monotherapy.

High-dose fianlimab combination showed a numerically higher median progression-free survival of 11.5 months compared to 6.4 months on Keytruda, but failed statistically with a p-value of 0.0627.

Low-dose combination showed a progression-free survival of 9.6 months, with a p-value of 0.4661.

No new safety signals were identified with the fianlimab combination.

The randomized, double-blind Phase 3 trial is investigating the combination of fianlimab and cemiplimab versus pembrolizumab in patients 12 years of age or older with unresectable locally advanced or metastatic melanoma who have not received a previous systemic treatment for advanced disease.


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Trial Design And Enrollment

The trial enrolled 1,546 patients to receive either:

  • 1600 mg fianlimab and 350 mg cemiplimab (high-dose combination).
  • 400 mg fianlimab and 350 mg cemiplimab (low-dose combination).
  • Placebo and 200 mg pembrolizumab or placebo and 350 mg cemiplimab.

Telix Partnership Expands Oncology Push

In April, Telix Pharmaceuticals Limited (NASDAQ:TLX) inked a significant collaboration announcement with Regeneron.

The partnership aims to develop next-generation radiopharmaceutical therapies, which could enhance Telix’s market position in precision oncology.

The company leverages its expertise in radiopharmaceutical development and manufacturing capabilities while sharing commercialization costs and profits with Regeneron.

REGN Price Action: Regeneron Pharmaceuticals shares were down 10.20% at $627.01 during premarket trading on Monday, according to Benzinga Pro.

Over the past month, REGN has declined about 16.4% versus a 4.3% rise in the S&P 500 and is down roughly 19% year-to-date compared to the index’s 7.8% gain.

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