Part 1 and Part 2: Number of Participants With Greater Than (>) 90% Bruton's Tyrosine Kinase (BTK) Occupancy

Part 1: Ibrutinib

Participants received ibrutinib based on age group and body surface area (BSA) in combination with chemoimmunotherapy (CIT) (investigator choice of RICE \[rituximab, ifosfamide, carboplatin, etoposide, and dexamethasone\]). For both regimens, triple intrathecal therapy consisting of methotrexate, corticosteroid, and cytarabine will be administered for central nervous system (CNS) prophylaxis in age-appropriate dosing. Ibrutinib suspension or capsule was administered once daily starting Day 1 Cycle 1. The first 2 participants enrolled in each age group (1-5 years, 6-11 years, and 12-17 years) received Ibrutinib at a lower starting dose of 240 milligram per meter square (mg/m\^2) (not to exceed 420 mg per day) for the first cycle (older children \[6-17 years\] were enrolled first before enrolling younger children \[1-5 years\]), followed by dose escalation to 329 mg/m\^2 (not to exceed 560 mg per day) at the start of Cycle 2 based on the safety assessments. The RICE regimen was composed of rituximab 750 mg/m\^2, ifosfamide 9 grams per meter square (g/m\^2), carboplatin 635 mg/m\^2, etoposide 300 mg/m\^2, and dexamethasone 100 mg/m\^2. Study treatment continued for 3 cycles (each cycle of 28 or 21 days), unless the participants experienced unacceptable toxicity or disease progression.

Part 2: Ibrutinib

Participants received ibrutinib based on age group and BSA in combination with CIT (investigator choice of RVICI \[rituximab, vincristine, ifosfamide, carboplatin, idarubicin, and dexamethasone\]). dexamethasone\]). For both regimens, triple intrathecal therapy consisting of methotrexate, corticosteroid, and cytarabine will be administered for central nervous system (CNS) prophylaxis in age-appropriate dosing. The first 2 participants enrolled in each age group (1-5 years, 6-11 years, and 12-17 years) received Ibrutinib at a lower starting dose of 240 mg/m2 (not to exceed 420 mg per day) for the first cycle (older children \[6-17 years\] were enrolled first before enrolling younger children \[1-5 years\]), followed by dose escalation to 329 mg/m2 (not to exceed 560 mg per day) at the start of Cycle 2 based on the safety assessments. The RVICI regimen was composed of rituximab 750 mg/m\^2, vincristine 1.6 mg/m\^2, ifosfamide 10 g/m\^2, carboplatin 800 mg/m\^2, idarubicin 20 mg/m\^2, and dexamethasone 100 mg/m\^2. Study treatment continued for 3 cycles (each cycle of 28 or 21 days), unless the participants experienced unacceptable toxicity or disease progression.

Analysis denominator · Participants