A Study to Evaluate the Efficacy and Safety of CC-93538 in Adult and Adolescent Japanese Participants With Eosinophilic Gastroenteritis

Induction Phase: Percentage of Participants Who Achieve Both Clinical and Histologic Response Composite at Week 16

Clinical response defined as percentage of participants who achieve \<4/15 in each of three Symptoms of Interest (Gastric Pain Symptoms domain, Stomach Heaviness Symptoms domain, and Diarrhea Symptoms domain) scores of Izumo Scale from baseline. Histologic response defined as a \> 75% reduction of peak gastric and/or duodenal eos count from baseline. Izumo Scale tests 5 different GI symptom domains during past week and consists with 15 weekly questions (3 questions per 1 domain): Heartburn Symptoms domain(Ques1 through3), Gastric Pain Symptoms domain(Questions4 through6), Stomach Heaviness Symptoms domain(Ques7 through9), Constipation Symptoms domain (Question 10 through12), Diarrhea Symptoms domain (Ques13 through15). Each question is scored on a 6-point Likert scale of "0 = No trouble at all" to "5 = Can't stand it," and score for each question within a domain added to determine domain specific scores scaled from 0 to 15, with higher values indicating greater symptom severity.

Time frame: Week 16

Induction + Maintenance: Percentage of Participants Who Achieve Both Clinical and Histologic Response Composite at Week 48

Clinical response defined as percentage of participants who achieve \<4/15 in each of three Symptoms of Interest (Gastric Pain Symptoms domain, Stomach Heaviness Symptoms domain, and Diarrhea Symptoms domain) scores of Izumo Scale from baseline. Histologic response defined as a \> 75% reduction of peak gastric and/or duodenal eos count from baseline. Izumo Scale tests 5 different GI symptom domains during past week and consists with 15 weekly questions (3 questions per 1 domain): Heartburn Symptoms domain(Ques1 through3), Gastric Pain Symptoms domain(Questions4 through6), Stomach Heaviness Symptoms domain(Ques7 through9), Constipation Symptoms domain (Question 10 through12), Diarrhea Symptoms domain (Ques13 through15). Each question is scored on a 6-point Likert scale of "0 = No trouble at all" to "5 = Can't stand it," and score for each question within a domain added to determine domain specific scores scaled from 0 to 15, with higher values indicating greater symptom severity.

Time frame: Baseline and week 48

Induction + Maintenance: Change From Baseline in Mean Number of Peak Eosinophils (Eos) Count Per High-power Field (Hpf) in Gastrointestinal (GI) Biopsies at Week 48

Blood samples were collected to assess eosinophils count. Baseline data are defined as last measurement collected on or prior the date of first dose for Induction Phase. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm

Time frame: Baseline and Week 48

Induction Phase: Percent Changes in Mean Number of Peak Eos Per Hpf in GI Biopsies From Baseline

Blood samples were collected to assess eosinophils count. Baseline data are defined as last measurement collected on or prior the date of first dose for Induction Phase.

Time frame: Baseline and Week 16

Induction + Maintenance: Percent Changes in Mean Number of Peak Eos Per Hpf in GI Biopsies From Baseline

Blood samples were collected to assess eosinophils count. Baseline data are defined as last measurement collected on or prior the date of first dose for Induction Phase. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: Baseline and Week 48

Induction Phase: Percentage of Participants With Eosinophil Histologic Response (> 75% Reduction)

Histologic response defined as a \> 75% reduction of peak gastric and/or duodenal eos count from baseline.

Time frame: Week 16

Induction + Maintenance: Percentage of Participants With Eosinophil Histologic Response (> 75% Reduction)

Histologic response defined as a \> 75% reduction of peak gastric and/or duodenal eos count from baseline. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: Week 48

Induction Phase: Percentage of Participants Who Achieve <4/15 in Each of Three Symptoms of Interest Scores Using the Izumo Scale

The Izumo Scale questionnaire assesses the comprehensive 5 different GI symptom domains during the past week and consists with 15 weekly questions (3 questions per 1 domain): Heartburn Symptoms domain(Questions1 through3), Gastric Pain Symptoms domain(Questions4 through6), Stomach Heaviness Symptoms domain(Questions7 through9), Constipation Symptoms domain (Question 10 through12), Diarrhea Symptoms domain (Questions13 through15). Each question is scored on a 6-point Likert scale of "0 = No trouble at all" to "5 = Can't stand it," and the score for each question within a domain is added to determine domain specific scores scaled from 0 to 15, with higher values indicating greater symptom severity. Gastric Pain Symptoms domain, Stomach Heaviness Symptoms domain, and Diarrhea Symptoms domain are Symptoms of Interest.

Time frame: Week 16

Induction + Maintenance: Percentage of Participants Who Achieve <4/15 in Each of Three Symptoms of Interest Scores Using the Izumo Scale

The Izumo Scale questionnaire assesses the comprehensive 5 different GI symptom domains during the past week and consists with 15 weekly questions (3 questions per 1 domain): Heartburn Symptoms domain(Questions1 through3), Gastric Pain Symptoms domain(Questions4 through6), Stomach Heaviness Symptoms domain(Questions7 through9), Constipation Symptoms domain (Question 10 through12), Diarrhea Symptoms domain (Questions13 through15). Each question is scored on a scale of "0 = No trouble at all" to "5 = Can't stand it," and one symptom domain is scored from 0 to 15, with higher values indicating greater symptom severity. Gastric Pain Symptoms domain, Stomach Heaviness Symptoms domain, and Diarrhea Symptoms domain are Symptoms of Interest. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm. Only participants from ages 12 -19 years old at specified timepoint are included in the analysis.

Time frame: Baseline and Week 48

Induction Phase: Changes in Total Score of Eosinophilic Gastrointestinal Disorder (EGID) Severity Score From Baseline to Weeks 16 in Adolescent (12 to 19 Years)

The EGID Severity Score for participants from 12 to 19 years old assesses 6 different symptoms (vomiting, dysphagia, anorexia, abdominal pain, diarrhea, bloody stool), 2 clinical laboratory tests (albumin, eos ratio of peripheral blood cells) and general condition, including height and weight. The score ranges from 0 to 100 and the higher the score, the greater the severity. A score of ≥ 40 is considered as severe, a score of 15 to 39 as moderate and ≤ 14 score as mild.

Time frame: Baseline and Week 16

Induction Phase: Changes in Total Score of EGID Severity Score From Baseline to Weeks 16 in Adults (>= 20 Years)

The EGID Severity Scores are assessed by the investigator. The EGID Severity Score for participants ≥ 20 years old assess the intensity and the frequency of 6 different symptoms (vomiting, dysphagia, anorexia, abdominal pain, diarrhea, bloody stool), 2 clinical laboratory tests (albumin, eos ratio of peripheral blood cells) and 2 medical history items (history of surgery and use of systemic corticosteroid or immunosuppressives). The score ranges from 0 to 82 and the higher the score, the greater the severity. A score of ≥ 40 is considered as severe, a score of 15 to 39 as moderate and a score of ≤ 14 score as mild.

Time frame: Baseline and Week 16

Induction+ Maintenance: Changes in Total Score of EGID Severity Score From Baseline to Weeks 48 in Adolescent (12 to 19 Years)

The EGID Severity Score for participants from 12 to 19 years old assesses 6 different symptoms (vomiting, dysphagia, anorexia, abdominal pain, diarrhea, bloody stool), 2 clinical laboratory tests (albumin, eos ratio of peripheral blood cells) and general condition, including height and weight. The score ranges from 0 to 100 and the higher the score, the greater the severity. A score of ≥ 40 is considered as severe, a score of 15 to 39 as moderate and ≤ 14 score as mild. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: Baseline and Week 48

Induction + Maintenance: Changes in Total Score of EGID Severity Score From Baseline to Weeks 48 in Adults (>= 20 Years)

The EGID Severity Scores are assessed by the investigator. The EGID Severity Score for participants ≥ 20 years old assess the intensity and the frequency of 6 different symptoms (vomiting, dysphagia, anorexia, abdominal pain, diarrhea, bloody stool), 2 clinical laboratory tests (albumin, eos ratio of peripheral blood cells) and 2 medical history items (history of surgery and use of systemic corticosteroid or immunosuppressives). The score ranges from 0 to 82 and the higher the score, the greater the severity. A score of ≥ 40 is considered as severe, a score of 15 to 39 as moderate and a score of ≤ 14 score as mild. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: Baseline and Week 48

Induction Phase: Time to First Event of Eosinophilic Gastroenteritis (EGE) Flare and First Use of Rescue Therapy

Any worsening of EGE symptoms during study participation will be documented as an EGE flare. Worsening of EGE symptoms is defined as continuous worsening of symptoms for 2 consecutive visits (4 weeks apart) compared to baseline, measured by the weekly Izumo Scale score (≥ 4 weeks of no change from baseline or ≥ 4 weeks of worsening from baseline).

Time frame: Through Week 16

Induction + Maintenance: Time to First Event of Eosinophilic Gastroenteritis (EGE) Flare and First Use of Rescue Therapy

Any worsening of EGE symptoms during study participation will be documented as an EGE flare. Worsening of EGE symptoms is defined as continuous worsening of symptoms for 2 consecutive visits (4 weeks apart) compared to baseline, measured by the weekly Izumo Scale score (≥ 4 weeks of no change from baseline or ≥ 4 weeks of worsening from baseline). Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: Through Week 48

Maintenance Phase: Time to Reduce to Zero Concomitant Corticosteroid Use

Participants who use concomitant corticosteroid at baseline and entered Maintenance Phase

Time frame: From Week 16 through Week 48

Percentage of Participants for Whom the Dose of Concomitant Steroids is Reduced to Zero

Participants who use concomitant corticosteroid at baseline and entered Maintenance period were included in the analysis.

Time frame: Week 24, 32, 40 and 48

Induction and Maintenance: Number of Participants With Treatment-Emergent Adverse Events

A treatment emergent adverse event (TEAE) is any AE that emerges during treatment or Safety Follow-up Period having been absent pre-treatment or worsens in severity relative to the pretreatment state. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: From Day 1 untill Week 48

Induction and Maintenance: Number of Participants With Remarkable Differences of Clinically Relevant Mean Changes From Baseline in Vital Signs Measurements

Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: From Day 1 untill Week 48

Induction and Maintenance: Number of Participants With Remarkable Differences of Clinically Relevant Mean Changes From Baseline in Physical Examinations Parameters

Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: From Day 1 untill Week 48

Induction and Maintenance: Number of Participants With Mean Changes Over Time That Were of Clinically Concern in Hematology Parameters, Serum Chemistry Parameters, and Urinalysis Parameters

Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: From Day 1 untill Week 48

Induction and Maintenance: Number of Participants With Anti-Drug-Antibody

Blood samples were collected to assess Anti-Drug-Antibody. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: From Day 1 till Week 48

Induction Phase: CC-93538 Trough Concentration at Week 16

Blood samples were collected to assess CC-93538 trough concentrations.

Time frame: Week 16

Maintenance Phase: CC-93538 Trough Concentration at Week 48

Blood samples were collected to assess CC-93538 trough concentrations. Participants that discontinued Induction period without entering maintenance period are included in the CC-93538 360 mg QW arm.

Time frame: Week 48