Alopecia areata (AA) is a chronic, relapsing T-cell mediated autoimmune disease characterized by nonscarring, typically patchy hair loss that affects people of all ages, races, and genders. In the United States (US), AA has an estimated point prevalence of 1.14% (Beningo et al., 2020). The three most common subtypes of AA are defined by the affected area:

• Patchy alopecia (PA), as seen in 90% of clinical diagnoses: hair loss occurring in one or more patches (ranging from coin-sized to large patches and even full scalp involvement) on the scalp or other parts of the body;
• Alopecia totalis (AT): loss of all or nearly all scalp hair;
• Alopecia universalis (AU): loss of all or nearly all scalp, face, and body hair Traditionally, a range of medications, including corticosteroids, immunotherapy, and minoxidil, are used to treat AA. However, few of these mainstay therapies are supported by robust clinical evidence, limiting the development of widely accepted clinical practice guidelines (Asfour et al., 2023). As a result of suboptimal effectiveness of traditional therapies, patients with AA, particularly those with extensive hair loss, have a persistent unmet medical need. Furthermore, the potential effects of AA on other subgroups, including patients with skin of color, remain undefined. As these subgroups have been historically underrepresented in clinical trials, an additional unmet medical need and evidence gap exists for these patients.

Recent clinical studies have demonstrated efficacy of novel treatments for AA, including ritlecitinib, a JAK3/TEC family kinase inhibitor developed and marketed by Pfizer (King et al., 2023). Ritlecitinib was approved by the US Food and Drug Administration (FDA) in June 2023 for the treatment of severe AA in adults and adolescents aged 12 years or older. Extensive information from clinical trials exists on the safety and efficacy of ritlecitinib, which, along with JAK inhibitors such as baricitinib and deuruxolitinib that are FDA approved for severe alopecia areas in adults 18 and over, have presented needed new therapeutic options for these patients. However, little is known about the clinical effectiveness of ritlecitinib in real-world clinical practice.

The objective of the current study is to evaluate patient characteristics, treatment patterns and related clinical outcomes of patients who initiated ritlecitinib to treat severe AA.

Inclusion criteria:

1. Confirmed diagnosis of severe AA (as determined by the treating physician)
2. Initiated ritlecitinib for severe AA between 01 July 2023 and 28 February 2025
3. At least 12 years of age at ritlecitinib initiation
4. Has at least one additional follow-up visit/consultation after ritlecitinib initiation in which scalp hair loss was assessed
5. Has a complete medical record regarding management or treatment of AA, covering the period initial AA diagnosis until their most recent follow-up/consultation

Exclusion criteria:

1. Ever diagnosed with other types of alopecia (i.e., e.g., chemotherapy-induced alopecia, androgenic alopecia [i.e., male pattern baldness], cicatricial alopecia [i.e., scarring alopecia], postpartum alopecia, or traction alopecia), other diseases (besides AA) that can cause hair loss, or other diseases that could interfere with assessment of hair loss/regrowth
2. No documentation in the medical record of percent of scalp hair loss
3. Participated in any clinical trial involving treatment with ritlecitinib, baricitinib, deuruxolitinib, delgocitinib, brepocitinib, or upadacitinib

The study will include patients with severe AA who initiated ritlecitinib (for treatment of severe AA) at least 6 months before the start of data collection. The study assumes that treatment with ritlecitinib was per label, as indicated for severe AA among patients at least 12 years of age. Data collection will be led by physicians (or their designated clinical assistants and staff, including nurse practitioners and physician assistants) recruited to the study who specialize in dermatology and are experienced in managing patients with AA.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.