Part 1 and Part 2: Overall Response Rate (ORR)

Part 1: Ibrutinib+RICE

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 1: Ibrutinib+RVICI

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.

Part 2: Ibrutinib+CIT (RICE or RVICI)

Participants received ibrutinib based on age group and BSA in combination with CIT (investigator choice of RICE or RVICI) until 3 treatment cycles, transplantation if indicated, or until progressive disease (PD) or unacceptable toxicity. 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. Participants of age groups 1-5 years and 6-11 years received ibrutinib 440 mg/m\^2, and age group 12-17 years received Ibrutinib 329 mg/m\^2 (dose selected from Part 1).

Part 2: Chemoimmunotherapy

Participants received CIT (investigator choice of RICE or RVICI) alone based on age group and BSA until 3 treatment cycles, transplantation if indicated, or until PD or unacceptable toxicity. For both regimens, triple intrathecal therapy consisting of methotrexate, corticosteroid, and cytarabine will be administered for CNS prophylaxis in age-appropriate dosing. The RICE regimen was composed of rituximab 750 mg/m\^2, ifosfamide 9 g/m2, carboplatin 635 mg/m\^2, etoposide 300 mg/m\^2, and dexamethasone 100 mg/m\^2. The RVICI regimen was composed of rituximab 750 mg/m\^2, vincristine 1.6 mg/m\^2, idarubicin 20 mg/m\^2, carboplatin 800 mg/m\^2, ifosfamide 10 g/m\^2, and dexamethasone 100 mg/m\^2 (all doses represented as cumulative administered in 1 cycle).

Analysis denominator · Participants