Why Is Apellis Pharmaceuticals (APLS) Stock Up +138% Today?

Key Takeaways

• APLS shares surged approximately +138.56% in premarket trading on March 31, 2026, from a prior close of $17.09 to a premarket price of approximately $40.77
• The primary catalyst is a definitive acquisition agreement announced by Biogen (BIIB), which agreed to acquire all outstanding shares of Apellis for $41.00 per share in cash, representing an upfront equity consideration of approximately $5.6 billion
• Shareholders will also receive a contingent value right (CVR) payable upon achievement of certain revenue thresholds tied to global net sales of SYFOVRE®
• The deal is expected to close in Q2 2026, subject to regulatory approvals and customary closing conditions
• The acquisition brings two commercialized immunology medicines — SYFOVRE® and EMPAVELI® — into Biogen's portfolio, which together generated $689 million in 2025 U.S. product revenue
• Traders are watching for shareholder approval, antitrust review outcomes, and any competing bids that could emerge ahead of the close

Opening Summary

Apellis Pharmaceuticals, Inc. (APLS) is a Waltham, Massachusetts-based biopharmaceutical company specializing in targeted complement therapies, best known for SYFOVRE® (pegcetacoplan intravitreal injection) for geographic atrophy and EMPAVELI® (pegcetacoplan subcutaneous injection) approved across three indications, including two rare kidney diseases. Shares of APLS surged approximately 138.56% in premarket trading on March 31, 2026, moving from a prior session close of $17.09 to roughly $40.77 — just below the $41.00 per share acquisition price agreed upon with Biogen (BIIB). The move is entirely acquisition-driven, with Biogen announcing a definitive agreement to purchase all outstanding APLS shares in an all-cash transaction valued at approximately $5.6 billion.

Biogen Acquisition Announcement

Biogen (BIIB) and Apellis jointly announced on the morning of March 31, 2026, that they have entered into a definitive merger agreement under which Biogen will acquire all outstanding shares of APLS for $41.00 per share in cash at closing, implying an upfront equity value of approximately $5.6 billion. In addition to the upfront cash consideration, APLS shareholders will receive a contingent value right (CVR) per share, which becomes payable if Apellis' flagship drug SYFOVRE® reaches certain global net sales milestones. The deal is expected to close in the second quarter of 2026, pending regulatory approvals and customary closing conditions.

Strategic Rationale

The acquisition is structured to strengthen Biogen's (BIIB) growth profile by adding two differentiated, revenue-generating immunology medicines. SYFOVRE®, approved for geographic atrophy — an immune-mediated retinal disease — achieved injection volume growth of 17% year-over-year in fiscal 2025 and currently holds a 60% market share in the geographic atrophy treatment category. EMPAVELI®, with FDA approval across three indications including C3G and IC-MPGN (rare kidney diseases), posted more than $102 million in 2025 U.S. revenues and had over 267 cumulative patient starts as of year-end 2025. Together, these products recorded $689 million in 2025 U.S. revenues and are expected to grow at a mid-to-high teen percentage rate at least through 2028.

Financial Impact on Biogen

Biogen (BIIB) stated that the transaction is expected to be increasingly accretive to non-GAAP diluted earnings per share beginning in 2027, and is projected to meaningfully increase Biogen's non-GAAP EPS compound annual growth rate (CAGR) through the end of the decade. Apellis' deep expertise in complement science is also expected to accelerate Biogen's entry into the nephrology space and enhance launch readiness for felzartamab, Biogen's own compound currently in Phase 3 clinical trials. Biogen views the combined commercialization capabilities of both organizations as key to maximizing the long-term potential of SYFOVRE® and EMPAVELI® globally.

Market Context and Trading Activity

Premarket volume for APLS spiked dramatically on the news, with approximately 157,000 shares trading in the premarket session alone — compared to an average premarket volume of roughly 9,158 shares over the prior 30 days, representing more than a 17-fold surge in early activity. The stock's premarket price of approximately $40.77 is trading at a very narrow discount to the $41.00 per-share acquisition price, as is typical in merger-arbitrage situations once a deal is announced at a fixed cash consideration. Broader biotech sector indices were not the driver here — the move is entirely idiosyncratic and deal-specific, driven by the acquisition premium over the prior $17.09 close.

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What Comes Next for APLS

With a definitive acquisition agreement in place at $41.00 per share, the primary variables for APLS shareholders now center on deal completion risk rather than fundamental operating performance. The transaction is expected to close in Q2 2026, and key milestones include receipt of antitrust clearance — particularly from the FTC and potentially international regulators — as well as an APLS shareholder vote. Should any regulatory challenges arise or a competing bid emerge, the share price dynamics could shift materially. The CVR tied to SYFOVRE® global net sales represents an additional potential payout for shareholders, and the outcome of SYFOVRE's prefilled syringe submission in the first half of 2026 could be relevant to that milestone. Until the transaction closes, APLS will continue reporting quarterly results, with analysts and market participants focused on maintaining commercial execution of SYFOVRE® and EMPAVELI® to support deal accretion projections.

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