CAMBRIDGE, Mass. — October 2, 2026
Biogen Inc. reported new 52-week Phase 2 data from the AMETHYST Phase 2/3 study showing continued improvements with investigational litifilimab in people living with cutaneous lupus erythematosus (CLE). The updated findings, presented at the European Academy of Dermatology and Venereology (EADV) 2026 Congress in Vienna, represent the longest dataset reported for litifilimab in CLE and showed sustained improvements in skin disease activity through Week 52. Among participants who received litifilimab from the beginning of the study, 27.2% achieved clear or almost clear skin at Week 52 compared with 19.0% at Week 24, while 28.8% achieved a CLASI-70 response compared with 21.7% at Week 24. Participants who switched from placebo to litifilimab also experienced improvements in skin disease activity as early as four weeks after treatment began.
Litifilimab Delivers Continued Skin Improvement
The AMETHYST Phase 2 study evaluated 93 adults with active CLE whose standard antimalarial treatments were ineffective or not tolerated. The 52-week results showed that treatment effects continued to improve over time, with more patients reaching clinically meaningful measures of skin clearance and disease activity reduction. The CLA-IGA-R endpoint showed that 27.2% of patients receiving litifilimab from the start achieved clear or almost clear skin at Week 52, compared with 19.0% at Week 24. On the CLASI-70 measure, 28.8% achieved at least a 70% reduction in disease activity at Week 52, compared with 21.7% at Week 24. Patients who crossed over from placebo to litifilimab at Week 24 showed an onset of improvement as early as four weeks, while 33.7% of these crossover participants had clear or almost clear skin by Week 52.
Targeted BDCA2 Approach Supports Lupus Development
Litifilimab, also known as BIIB059, is an investigational monoclonal antibody designed to selectively target BDCA2 receptors on plasmacytoid dendritic cells (pDCs), which are involved early in the inflammatory processes associated with CLE. Biogen is developing the therapy as a potential once-monthly treatment intended to reduce inflammation at its source. The company received FDA Breakthrough Therapy Designation for litifilimab in CLE in January 2026, while previous Phase 2 LILAC results demonstrated reduced skin disease activity compared with placebo. Litifilimab remains investigational and has not been approved by any regulatory authority, meaning the current findings do not establish regulatory approval or confirmed clinical effectiveness. The AMETHYST program is designed to further evaluate the candidate in patients with active subacute and/or chronic CLE who are refractory or intolerant to antimalarial therapy.
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Phase 3 AMETHYST Results Expected in 2027
The longer-term data also showed a consistent safety profile, with no new safety signals identified during the 52-week treatment period. Most adverse events were mild or moderate, while serious adverse events occurred in 3.4% of participants during the extended treatment period; commonly reported adverse events included nasopharyngitis, influenza and arthralgia. The Phase 3 portion of AMETHYST remains blinded, with results expected in the first half of 2027. AMETHYST is a randomized, double-blind, placebo-controlled Phase 2/3 study evaluating litifilimab in patients with active CLE, with treatment administered subcutaneously every four weeks following an initial additional dose at Week 2. The ongoing Phase 3 program will provide further evidence on the efficacy and safety of litifilimab and represents the next major clinical milestone for Biogen’s CLE development strategy.
Source: Biogen,,, press release
