Litifilimab (BIIB059) - (AMETHYST)

October 2, 2026: Biogen (NASDAQ: BIIB) reported 52-week Phase 2 Part A data from the ongoing AMETHYST Phase 2/3 study of litifilimab (BIIB059) in cutaneous lupus erythematosus (CLE) at the EADV 2026 Congress. In 93 adults with active SCLE and/or CCLE refractory or intolerant to antimalarials, patients treated with litifilimab from baseline showed continued improvement from week 24 to week 52: 27.2% achieved clear/almost clear skin by CLA-IGA-R erythema score 0/1 versus 19.0% at week 24, and 28.8% achieved CLASI-70 versus 21.7% at week 24. Patients who crossed over from placebo to litifilimab at week 24 showed improvement as early as four weeks; by week 52, 33.7% had clear/almost clear skin.

Safety was consistent with prior Phase 2 studies, with no new safety signals. Serious adverse events occurred in 3.4% (3/88) during the extended treatment period; the most common adverse events (at least 5%) were nasopharyngitis, influenza, and arthralgia.

The Phase 3 AMETHYST study (NCT05531565) remains blinded, with results expected in the first half of 2027. The release also states the FDA granted Breakthrough Therapy Designation to litifilimab for CLE in January 2026.