- Design
- Phase 2 part of a randomised, double-blind, placebo-controlled phase 2/3 study
- Population
- Adults with cutaneous lupus erythematosus
- Primary outcome
- Clear or almost clear erythema (CLA-IGA-R 0-1) at week 16
- Effect
- 14.7% vs 2.9% (P=.026); CLASI-70 at week 24 21.7% vs 5.8%
AMETHYST Part A (JAAD, 17 October 2026) randomised patients with cutaneous lupus erythematosus to litifilimab 225 mg or placebo every four weeks for 24 weeks. Litifilimab is a monoclonal antibody against BDCA2 on plasmacytoid dendritic cells, which drive type I interferon in lupus skin.
At week 16, 14.7% on litifilimab reached clear or almost clear erythema on the investigator global assessment, against 2.9% on placebo (P=.026). At week 24, CLASI-70 responses were 21.7% versus 5.8%. Tolerability was in line with earlier studies.
Cutaneous lupus has no approved targeted therapy, and many patients cycle through antimalarials, topical steroids and off-label immunosuppressants. This is a real signal for a mechanism-based treatment, but the absolute response rates are modest and the trial is phase 2. The phase 3 part of the programme will decide whether it reaches the clinic.
For now, nothing changes in practice: optimise hydroxychloroquine, photoprotection and smoking cessation, and consider referral to a trial for refractory disease.
- Keep hydroxychloroquine, strict photoprotection and smoking cessation as the base of cutaneous lupus care
- Consider trial referral for patients refractory to antimalarials
- Expect modest absolute response rates - most patients on litifilimab did not reach clear skin
- Use CLASI scoring at reviews so trial-level responses are interpretable locally
Why it matters
Cutaneous lupus has had no targeted therapy, and this mechanism is now showing clinical effect.
Don't overread it
Phase 2 evidence with modest absolute responses - the drug is not approved and phase 3 is pending.
The statistics, in plain English
14.7% versus 2.9% is a meaningful relative difference, but in absolute terms about one extra patient in eight or nine reached clear skin. The P value of .026 shows the difference is unlikely to be chance, and the secondary CLASI-70 endpoint was not powered for significance.
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