A proof-of-concept open-label clinical trial of spleen tyrosine kinase antagonism using fostamatinib in moderate-to-severe hidradenitis suppurativa

Background: Hidradenitis suppurativa (HS) is an autoinflammatory disorder of keratinization with a prominence of B cells and plasma cells. Fostamatinib is a spleen tyrosine kinase inhibitor targeting B cells and plasma cells.Objectives: To assess the safety, tolerability, and clinical response at week 4 and week 12 of fostamatinib in moderate-to-severe HS. Methods: Twenty participants were administered fostamatinib 100 mg twice a day for 4 weeks, escalating to 150 mg twice a day thereafter until week 12. Participants were assessed for adverse events and clinical response assessed by HiSCR (Hidradenitis Suppurativa Clinical Response Score) and IHS4 (International Hidradenitis Suppurativa Severity Score) as well as other outcomes including DLQI (Dermatology Life Quality Index), visual analog scale, and physician global assessment.Results: All 20 participants completed the week 4 and week 12 endpoints. Fostamatinib was well tolerated in this cohort with no grade 2/3 adverse events reported. A total of 85% achieved HiSCR at week 4 and 85% at week 12. The greatest reduction in disease activity was seen at weeks 4/5 with worsening in a proportion of patients thereafter. Significant improvements were seen in pain, itch, and quality of life.Conclusions: Fostamatinib was well tolerated in this HS cohort with no serious adverse events and improvement in clinical outcomes. Targeting B cells/plasma cells may be a viable therapeutic strategy in HS and requires further exploration.