Shares of ChemoCentryx Inc. plunged 44.8% in trading on Tuesday after the Food and Drug Administration questioned the rationale behind some of the clinical data for avacopan, an experimental treatment for a rare autoimmune disease. The document was released in advance of a FDA advisory committee scheduled for Thursday. ChemoCentryx is seeking approval for avacopan as a treatment for anti-neutrophil cytoplasmic auto-antibody-associated vasculitis. Joseph Schwartz, an analyst for SVB Leerink, told investors that the “FDA briefing documents are surprisingly critical and suggest that CCXI has an uphill battle,” noting that the regulator’s stance in the briefing document was a surprise. Raymond James analyst Steven Seedhouse also described his surprise at the FDA’s decision to question the investigational therapy’s safety and efficacy; however, he still expects a positive decision from the committee. ChemoCentryx’s stock is down 56.6% for the year, while the broader S&P 500 is up 11.6%.

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