INCB054707

Adverse events either reported for the first time in this Protocol or any AE ongoing and defined as treatment-emergent from the parent Protocol.

Defined as proportion of participants achieving a ≥ 4-point improvement \[reduction\] in Itch NRS score from baseline (Itch NRS4) and an IGA CPG-S score of 0 or 1 with a ≥ 2-grade improvement from baseline (IGA-CPG-S-TS).

≥75% improvement in facial Vitiligo Area Scoring Index.

HiSCR is defined as at least a 50% reduction from baseline in the total abscess and inflammatory nodule count, with no increase from baseline in abscess or draining tunnel count.

The UAS7 is defined as the 7-day sum of the individual, daily recorded scores for the hive severity score (HSS) and the itch severity score (ISS). The ISS7 is defined as the 7-day sum of the daily ISS scores (ranging from 0 to 3), and the HSS7 is defined as the 7-day sum of the daily HSS scores (ranging from 0 to 3). The UAS7 score is calculated as the sum of the available UAS scores, divided by the number of days that have a UAS score, multiplied by 7. The UAS7 (ranging from 0 to 42) is equal to the ISS7 (ranging from 0 to 21) plus the HSS7 (ranging from 0 to 21). Higher scores represent more intense/severe hives and itching. Change from baseline was calculated as the post-baseline value minus the baseline value.

To assess the effect of povorcitinib on lung function (pre-BD FEV1) between baseline and week 24

Each evening, the participants assessed their worst level of itch during the past 24 hours on a scale of 0 (no itch) to 10 (worst itch imaginable). The Baseline Itch NRS score was determined by averaging the 7 daily Itch NRS scores before Day 1 (i.e., Day -7 to Day -1). If ≥4 of the 7 days of the daily Itch NRS scores were missing prior to Day 1, then the Baseline Itch NRS score was set to "missing." The by-visit Itch NRS score for postbaseline visits was determined by averaging the 7 daily Itch NRS scores before the visit day. If 4 or more daily Itch NRS scores out of the 7 days before the visit day were missing, the Itch NRS score at the visit was set to missing.

The T-VASI was calculated based on values from the whole body, which was split into 6 separate and mutually exclusive regions (possible range: 0-100; higher values=worse outcome). The percentage of vitiligo involvement was estimated in hand units (% body surface area \[BSA\]; investigator assessed), based on the participant's hand size. The degree of depigmentation for each body site was determined and estimated to the nearest percentage: 0%, 10%, 25%, 50%, 75%, 90%, or 100%. The T-VASI was derived by multiplying the values assessed for the vitiligo involvement by the percentage of affected skin for each body site and summing the values of all body sites. Percent change was calculated as (\[post-Baseline value minus the Baseline value\] / Baseline value) x 100.

Change from Baseline was calculated as the post-Baseline value minus the Baseline value. The mixed model repeated measure (MMRM) included the fixed effects of treatment group (placebo and INCB054707 15, 45, and 75 mg), stratification factors (disease severity \[Hurley Stage I, II, and III\] and geographical region \[North America and outside of North America\]), visit (Weeks 2, 4, 6, 8, 12, and 16), treatment by visit interaction, and covariates of Baseline measurement and Baseline measurement by visit interaction. The variance-covariance matrix of the within-participant errors in MMRM are modeled as unstructured.

TEAE is defined as any adverse event either reported for the first time or worsening of a pre-existing event after first dose of study drug. Grading was performed using guidance from the CTCAE v 4.03. A grade 3 and above would constitute as "severe".

A TEAE is any adverse event (AE) either reported for the first time or worsening of a pre-existing event after first dose of study drug.

Defined as maximum observed plasma concentration of INCB054707

Area Under the concentration- time curve up to the last measurable concentration of INCB054707

Defined as under the concentration-time curve up to the last measurable concentration of INCB054707

Defined as maximum observed plasma concentration of INCB054707

Defined as the area under the concentration- time curve up to the last measurable concentration of INCB54707.

Defined as area under the concentration-time curve From 0 to Infinity of INCB054707