FDA's Withdrawal Proposal

Amgen faces a significant regulatory challenge as the FDA proposes withdrawing its rare disease drug Tavneos (avacopan). The FDA's move suggests a major disagreement over the drug's effectiveness and the honesty of its application data, potentially affecting investor confidence and Amgen's pipeline.

Alleged Data Deception

The U.S. Food and Drug Administration (FDA) has formally proposed the withdrawal of Amgen's Tavneos (avacopan). In a letter dated April 27, 2026, the FDA stated it "can no longer conclude that there is, or has ever been, a valid demonstration of substantial evidence of effectiveness for TAVNEOS." The agency's main argument centers on "new information, which was withheld from FDA and did not become known to FDA until more than three years after approval, indicating that there is a lack of substantial evidence of effectiveness for the drug, and the application contains untrue statements of material facts." Specifically, the FDA raised concerns about the process followed by original sponsor ChemoCentryx to re-adjudicate primary endpoint results for nine of the 331 patients in the pivotal ADVOCATE trial. Amgen, which acquired ChemoCentryx in October 2022, denies awareness of issues with the underlying patient data.

Escalating Safety Alarms

Beyond efficacy, serious safety concerns have emerged. In March 2026, the FDA identified 76 cases of drug-induced liver injury (DILI) with evidence suggesting a causal link to Tavneos. This includes seven instances of vanishing bile duct syndrome (VBDS), a condition that can lead to permanent liver damage. Eight deaths were reported among these cases. On March 31, 2026, the FDA issued a Drug Safety Communication (DSC) detailing these serious postmarketing cases of DILI, many reported outside the U.S., primarily from Japan. While hepatotoxicity is a known risk with a warning on the drug's label, the DSC highlighted VBDS as a significant concern.

Market Impact and Financials

Amgen has stated it does not intend to voluntarily withdraw Tavneos, informing the FDA of this decision on January 28, 2026, following an initial request on January 16, 2026. This has created a standoff. Tavneos generated $71 million in the second quarter of 2024 and $459 million for the full year 2025, representing approximately 1.2% of Amgen's revenue. Projections anticipated around $600 million in sales for 2026, with a peak sales forecast of $1.2 billion by 2031. The company's stock, trading around $344.60 on April 28, 2026, has a market capitalization of approximately $185.77 billion and a trailing P/E ratio near 24.79. Amgen reported strong 2025 financials with $36.8 billion in total revenues (10% growth) and anticipates 2026 revenues between $37 billion and $38.4 billion. However, the potential loss of Tavneos presents a significant challenge to its rare disease portfolio.

Competitive Landscape

Tavneos is an oral complement C5a receptor antagonist approved for severe active ANCA-associated vasculitis (AAV), a group of rare autoimmune diseases. The treatment landscape includes established biologics like rituximab, which is highly effective and often preferred for remission induction and maintenance. For EGPA, Nucala (mepolizumab) and Fasenra (benralizumab) are approved. Emerging therapies and investigational agents also target pathways such as BAFF and IL-5. Given the safety concerns and efficacy questions, patients and physicians might increasingly opt for established alternatives, especially with competitive pressures in the AAV market.

Credibility and Risk Concerns

The FDA's explicit allegations of withheld information and "untrue statements of material facts" directly challenge Amgen's credibility. This suggests potential misrepresentation dating back to the drug's development by ChemoCentryx, which Amgen acquired for billions. The significant safety profile, including fatal liver injuries and vanishing bile duct syndrome, presents an undeniable risk to patients and introduces substantial liability. The European Medicines Agency is also re-reviewing Tavneos' data integrity. Losing a drug with projected peak sales of $1.2 billion, coupled with the reputational damage from alleged data integrity issues, could lead to greater investor skepticism towards Amgen's future pipeline approvals and acquisitions. Intensifying regulatory scrutiny in the biotech sector makes such disclosures particularly damaging.

Outlook

The situation remains fluid as Amgen reviews its next steps with the FDA, while emphasizing patient safety. The agency has advised healthcare professionals to discuss Tavneos and alternative treatments with patients while a final decision is pending. Given the FDA's firm stance and growing safety data, Tavneos' long-term presence on the U.S. market appears increasingly uncertain, potentially affecting Amgen's revenue targets and rare disease division outlook.