Pfizer Inc. announced the initiation of a Phase 2b/3 clinical trial for its oral JAK3 inhibitor, PF-06651600, for the treatment of patients with moderate to severe alopecia areata, a chronic autoimmune skin disease that causes hair loss on the scalp, face, or body, and currently has no approved therapies. Positive Phase 2a data for PF-06651600 was recently presented as a late-breaker at the 27th European Academy of Dermatology and Venerology (EADV). The study met the primary efficacy endpoint in improving hair regrowth on the scalp relative to baseline at week 24 as measured by the Severity of Alopecia Tool (SALT) score (100 point scale). In addition to meeting the primary efficacy endpoint, the investigational candidate also met all secondary endpoints in the study. Overall, adverse event (AE) rates were comparable between treatment groups. The most common AEs seen in the study were in the infections, gastrointestinal and skin/subcutaneous tissue categories. There were no cases of herpes zoster reactivation. Based on the totality of the data and the emerging clinical profile, PF-06651600 was granted Breakthrough Therapy designation from U.S. FDA for the treatment of alopecia areata in September 2018. PF-06651600 will also continue to be evaluated for rheumatoid arthritis, Crohn’s disease and ulcerative colitis. The pivotal trial will enroll an estimated 660 patients and will be a double-blind, placebo-controlled, dose-ranging study to evaluate the safety and effectiveness of PF-06651600 in adults and adolescents (12 years and older) who have 50% or greater scalp hair loss.