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Introduction: Baricitinib, an oral Janus kinase (JAK)1/JAK2 inhibitor, is indicated in the European Union and Japan for treatment of moderate-to-severe atopic dermatitis (AD) in adults who are candidates for systemic therapy. In the ongoing, placebo-controlled, phase 3 trial BREEZE-AD5, once-daily oral baricitinib 2-mg monotherapy improved disease in moderate-to-severe AD patients who had an inadequate response or intolerance to topical corticosteroids. This post-hoc analysis aimed to identify responders to baricitinib 2 mg, using a proposed clinical tailoring approach based on baseline body surface area (BSA) affected and early clinical improvement, in BREEZE-AD5. Methods: Classification and regression tree method was used to evaluate baseline predictors for the proportion of patients achieving ≥ 75% improvement in Eczema Area and Severity Index (EASI75) at week 16 among baricitinib 2-mg-treated patients. Two-by-two contingency tables evaluated the association between early response, defined as ≥ 50% improvement in BSA or ≥ 3-point improvement in Itch Numeric Rating Scale from baseline at weeks 4 or 8, and response at week 16 for the proportion of patients achieving EASI75, validated Investigator Global Assessment for AD (vIGA-AD) score of 0 or 1, or ≥ 4-point improvement in Itch (Itch ≥ 4), respectively. Missing data were imputed as non-responder. Results: At week 16, EASI75 and vIGA-AD (0,1) were achieved by 37.5% and 31.7% of baricitinib 2-mg-treated patients with baseline BSA 10–50% compared with 9.5% and 4.8% with BSA > 50%. Early response in skin inflammation or itch at week 4 was associated with corresponding EASI75, vIGA-AD (0,1), and Itch ≥ 4 of 55.4%, 48.2%, and 39.3% at week 16, while early response at week 8 was associated with 66.7%, 56.1%, and 42.1% of patients achieving these endpoints. Conclusion: Baseline BSA of 10–50% and early clinical improvement after 4 or 8 weeks of baricitinib 2-mg treatment may identify patients most likely to benefit from long-term baricitinib 2-mg therapy. Clinical Trial Registration: NCT03435081. Plain Language Summary: Baricitinib is a medication that helps a dysregulated immune system readjust. This leads to improvements in the inflammatory disease atopic dermatitis (AD). Baricitinib is approved for adults with moderate-to-severe AD in over 40 countries. In the ongoing study BREEZE-AD5, baricitinib 2 mg improved moderate-to-severe AD in patients who previously did not respond to or could not tolerate topical corticosteroids. Understanding which patients are likely to benefit most from a medication can improve patient experience with treatment. It can also ensure that only patients who are likely to benefit from a medication are exposed to it. This analysis aimed to identify patients who are most likely to benefit from baricitinib 2 mg in BREEZE-AD5, using an approach based on baseline body surface area (BSA) affected and early clinical improvement. We showed that patients with moderate-to-severe AD affecting between 10% and 50% of their BSA account for the majority of patients who respond to baricitinib 2 mg after 16 weeks of treatment. Clinical assessment of skin inflammation or itch in patients after 4–8 weeks of initiation of baricitinib 2-mg treatment further improved the ability to identify patients who are most likely to benefit from long-term therapy. This proposed clinical tailoring approach of baseline BSA of 10–50% and early clinical improvement after 4 or 8 weeks of baricitinib 2-mg treatment may allow for the treatment of patients who are most likely to respond to therapy, and rapid decision on discontinuation of treatment for those who are not likely to benefit from baricitinib 2 mg. [ABSTRACT FROM AUTHOR]