Inclusion Criteria:

St. Jude Participants:

1. Participant must have a histologic diagnosis of a mature B cell lymphoma (e.g.,
Burkitt lymphoma/leukemia, atypical Burkitt lymphoma, diffuse large B-cell lymphoma,
mediastinal large B-cell lymphoma, mature B-cell lymphoma NOS) as defined in the WHO
classification.

2. Participant must be previously untreated, (no more than 72 hours of steroids and/or
emergency radiation)

3. Participant must be < 22 years of age at the time of diagnosis

4. For Group B participants with mediastinal large B cell lymphoma (MLBCL) disease only
(receiving rituximab) - Hepatitis screening has been obtained. This screening must
be done for eligibility BUT the results are not needed prior to enrollment:

- Hepatitis B immunization status (vaccination Yes or No)

- HBsAg

- Anti-HBs antibody

- Anti-HBc antibody. All participants must have screening prior to enrollment.
Participants whose results indicate that they are carrier of hepatitis B can
still be treated per Group B but will NOT receive rituximab.

5. HIV test has been obtained within 42 days. Participants who test positive for HIV
cannot be enrolled on therapeutic part of study, but are still eligible for biology
studies.

6. Informed consent must be obtained according to St. Jude guidelines before enrollment
into study

Participants from Collaborating Sites Participating in Biological Objectives Only:

1. Participant must have a histologic diagnosis of a mature B cell lymphoma (e.g.,
Burkitt lymphoma/leukemia, atypical Burkitt lymphoma, diffuse large B-cell lymphoma,
mediastinal large B-cell lymphoma, mature B-cell lymphoma NOS) as defined in the WHO
classification

2. Participant must be < 22 years of age at the time of diagnosis

3. Informed consent must be obtained by local PI or his/her designee according to
ICH/Good Clinical Practice and local guidelines before enrollment into study

Exclusion Criteria:

Participants from Collaborating Sites Participating in Therapeutic and Biological
Objectives:

1. Participants with prior therapy (except steroids or RT)

2. Participants known to be HIV positive (for therapeutic part of protocol, HIV
participants are eligible for biology studies).

3. Participants who are pregnant or lactating

4. Inability or unwillingness of research participant or legal guardian to consent

5. Participants who received emergent steroids and/or radiation prior to biopsy may be
included in therapeutic part of study, but will be excluded from biology studies.

Participants from Collaborating Sites Participating in Biological Objectives Only:

1. Inability or unwillingness of research participant or legal guardian to consent

2. Histologic diagnosis other than a mature B-cell lymphoma as defined in the WHO
classification

3. Participants who received emergent steroids and/or radiation prior to biopsy