On June 9, Regeneron Pharmaceuticals declined 3.07% in regular trading, trading at $616.05/share, with trading volume of $158 million. Multiple negative catalysts converged to pressure the stock.

On the clinical front, Regeneron disclosed that its closely watched Phase 3 trial evaluating fianlimab combined with cemiplimab as first-line therapy for unresectable locally advanced or metastatic melanoma failed to achieve statistical significance on its primary endpoint. The randomized, double-blind trial enrolled 1,546 previously untreated advanced melanoma patients across four treatment arms.

Simultaneously, Icelandic biopharma company Alvotech, in partnership with Teva, resubmitted a biologics license application to the FDA for AVT06, a biosimilar to Regeneron's core product Eylea. Clinical data showed AVT06 demonstrated equivalent efficacy in best-corrected visual acuity changes with comparable safety profiles, intensifying market concerns over revenue erosion in Regeneron's ophthalmology franchise. The broader biotech sector also traded lower, with AbbVie down 2.37%, Gilead Sciences down 1.45%, and Amgen down 1.20%.

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