argenx Reports Topline Results from ADDRESS Study of Efgartigimod SC in Pemphigus

• ADDRESS study did not meet primary or secondary endpoints
• Pemphigus deprioritized as efgartigimod indication
• Update on BALLAD study GO/NO GO decision
• Conference call scheduled for today, December 20, 2023, at 8:30am ET (2:30pm CET)

Regulated Information – Inside Information

December 20, 2023, 7:00am CET

AMSTERDAM, THE NETHERLANDS — argenx SE (Euronext & Nasdaq: ARGX), a global immunology company committed to improving the lives of people suffering from severe autoimmune diseases, today announced topline results from the ADDRESS study evaluating efgartigimod subcutaneous (SC) (efgartigimod alfa and hyaluronidase-qvfc) in adults with pemphigus vulgaris (PV) and pemphigus foliaceus (PF). The ADDRESS results show the proportion of PV patients achieving the primary endpoint of complete remission on a minimal dose of steroids (CRmin) was not significantly different between efgartigimod SC and placebo.

argenx will not pursue additional development in pemphigus and plans to prioritize clinical development of efgartigimod in its ongoing severe autoimmune indications.

“We are disappointed by today’s results, particularly for pemphigus patients who have seen little innovation in this treatment space,” said Luc Truyen, M.D., Ph.D., Chief Medical Officer at argenx. “At argenx, we are in the business of transformation, providing new medicines that go beyond incremental benefit and raise the bar for what patients can expect from a treatment. While we will not move forward into pemphigus, our job today is the same as yesterday – continue to be execution-focused and data-driven, apply learnings across our ongoing development programs, and pursue optimal development of efgartigimod, empasiprubart and our earlier stage programs. 2023 was a remarkable year of growth for argenx across the business and we are poised to build on our success in 2024.

“We are grateful to the pemphigus community and all involved in the ADDRESS study, including patients, healthcare professionals, and our argenx teams,” continued Dr. Truyen.

ADDRESS Study Results

The Phase 3 ADDRESS study enrolled 222 adult patients with newly diagnosed or relapsing moderate-to-severe PV (n=190) or PF (n=32). Patients were randomized to efgartigimod SC or placebo with both treatment groups receiving concomitant steroids at a starting dose of 0.5mg/kg, which is a lower dose than recommended by current treatment guidelines and was tapered according to protocol upon achievement of complete remission.