TL;DR: Biogen said on Oct. 2, 2026 that litifilimab produced durable skin improvement through 52 weeks in the Phase 2 part of the AMETHYST study in cutaneous lupus erythematosus.
Biogen reports 52-week skin-clearance results
Biogen Inc. said on Friday, Oct. 2, 2026 that its experimental drug litifilimab showed durable improvement in skin symptoms among patients with cutaneous lupus erythematosus in a mid-stage study, according to Reuters in "Biogen's experimental lupus drug shows benefit against skin symptoms".
The update covers the Phase 2 portion of the ongoing AMETHYST Phase 2/3 study, designated Part A, according to Biogen's announcement carried by GlobeNewswire in "Biogen’s Litifilimab Demonstrates Rapid and Durable Efficacy in New 52-Week Phase 2 Data".
Biogen presented the 52-week results at the European Academy of Dermatology and Venereology 2026 Congress in Vienna, Austria, according to that company announcement.
The company described the dataset as the longest reported for litifilimab in cutaneous lupus erythematosus, according to the same announcement.
Cutaneous lupus erythematosus can cause painful rashes, sensitivity to sunlight, hair loss, skin discoloration and permanent scarring, according to Reuters.
There are no approved targeted treatments for the condition, according to Reuters.
Who was studied in AMETHYST Part A
The Phase 2 portion evaluated 93 adults with active skin symptoms for whom standard antimalarial medications were not effective or not tolerable, according to Biogen's announcement.
The study was randomized, double-blind and placebo-controlled, according to reporting by Practical Dermatology in "Litifilimab Meets Primary Endpoint in Phase 2 Cutaneous Lupus Study".
It compared subcutaneous litifilimab plus standard of care with placebo plus standard of care, according to Practical Dermatology.
Part A assessed outcomes through week 24 in its initial controlled period, while follow-up continued through week 52, according to Practical Dermatology and Biogen's announcement.
The Phase 3 portion remains ongoing and blinded, according to Practical Dermatology.
Clear-skin responses increased between week 24 and week 52
Among participants who received litifilimab from the beginning of the trial, 27.2% had clear or almost clear skin after one year, compared with 19% after 24 weeks, according to Reuters.
The measure was a Cutaneous Lupus Activity Investigators' Global Assessment Revised erythema score of 0 or 1, referred to as CLA-IGA-R 0-1, according to Biogen's announcement.
The announcement said 19.0% of that continuous-litifilimab group had reached CLA-IGA-R 0-1 at week 24 and 27.2% had reached it by week 52.
A second skin-activity measure also increased over the same interval, according to the announcement.
That measure was a 70% or greater reduction in Cutaneous Lupus Erythematosus Disease Area and Severity Index Activity, called CLASI-70, according to the announcement.
In the continuous-litifilimab group, 21.7% achieved CLASI-70 at week 24 and 28.8% achieved it at week 52, according to the announcement.
Earlier 16-week and 24-week endpoints
At week 16, 14.7% of patients receiving litifilimab achieved a CLA-IGA-R erythema score of 0 or 1, compared with 2.9% receiving placebo, according to Practical Dermatology.
The difference was 11.8 percentage points, with a 95% confidence interval of 1.39 to 22.27 and P less than .05, according to Practical Dermatology.
Practical Dermatology reported that Phase 2 Part A met its primary endpoint at that week-16 assessment.
At week 24, CLASI-50 response was achieved by 40.8% of litifilimab-treated participants compared with 21.0% receiving placebo, according to Practical Dermatology.
CLASI-70 responses at week 24 were reported in 21.7% and 5.8%, respectively, according to Practical Dermatology.
Those secondary endpoints were not adjusted for multiplicity and therefore cannot demonstrate statistical significance, according to Practical Dermatology.
Rapid response after switch from placebo
Participants who started the study on placebo and transitioned to litifilimab halfway through experienced rapid onset of benefit, according to Biogen's announcement.
Skin symptoms began to improve as early as four weeks after the switch, according to the announcement.
Biogen said that early timing was consistent with results seen in participants who started on litifilimab and were reported earlier this year, according to the announcement.
By week 52, approximately one in three of these crossover participants, or 33.7%, had clear or almost clear skin, according to the announcement.
Study investigator Victoria Werth, M.D., told Practical Dermatology that patients initially assigned to placebo who later received litifilimab improved quickly during the extension period.
“They were already getting better within 2 to 4 weeks,” she said, according to Practical Dermatology.
Werth also said durability was sustained over the interval between 24 and 52 weeks for patients who initially received litifilimab, according to Practical Dermatology.
How litifilimab is designed to work
Litifilimab is a humanized IgG1 monoclonal antibody targeting blood dendritic cell antigen 2, known as BDCA2, according to Practical Dermatology.
Biogen is evaluating it as a potential once-monthly, first-in-class treatment, according to Biogen's announcement.
The approach is designed to reduce inflammation at its source by selectively targeting BDCA2 receptors on plasmacytoid dendritic cells, according to the announcement.
Those cells, abbreviated pDCs, play a central role early in the inflammatory process in cutaneous lupus erythematosus, according to the announcement.
Litifilimab is also being tested for lupus and other forms of the autoimmune condition, according to Reuters.
Safety through 52 weeks
Over the 52-week treatment period, litifilimab was generally well tolerated with a safety profile consistent with previously reported Phase 2 studies, according to Biogen's announcement.
No new safety signals were identified, according to the announcement.
The majority of adverse events reported were mild or moderate in severity, according to the announcement.
Serious adverse events occurred in 3.4%, or 3 of 88 participants, during the extended treatment period, according to the announcement.
The most common adverse events during the extended treatment period, each at 5% or more, were nasopharyngitis, influenza and arthralgia, according to the announcement.
Through week 24, adverse events had occurred in 74.6% of patients receiving litifilimab and 64.7% receiving placebo, with most classified as mild to moderate, according to Practical Dermatology.
Serious adverse events through week 24 occurred in 6.8% and 2.9%, respectively, according to Practical Dermatology.
Regulatory status and next expected readout
In January 2026, litifilimab was granted Breakthrough Therapy Designation by the U.S. Food and Drug Administration for treatment of cutaneous lupus erythematosus, according to Biogen's announcement.
Results from the Phase 3 part of AMETHYST are expected in the first half of 2027, according to the announcement.
The company said the 52-week Phase 2 findings further support litifilimab's potential to achieve rapid and durable improvements in skin disease activity, according to the announcement.
Biogen Chief Medical Officer Daniel Quirk, M.D., said the data reinforce litifilimab's potential to deliver rapid improvement and demonstrate durable skin-clearance effects, according to the announcement.
Dermatologist and rheumatologist Joseph F. Merola, M.D., said it was highly encouraging to see continued improvement in skin clearance with over a quarter reaching clear or almost clear skin, according to the announcement.