Inclusion Criteria:

- Histologically proven Primary Mediastinal Large B-Cell Lymphoma (PMLBL).

- PMLBL without central nervous system (CNS) involvement.

- 6 months to less than 18 years of age at the time of consent.

- Males and females of reproductive potential must agree to use an effective
contraceptive method during the treatment, and after the end of treatment: during
twelve months for women, taking into account the characteristics of rituximab

- Complete initial work-up within 8 days prior to treatment that allows definite
staging.

- Able to comply with scheduled follow-up and with management of toxicity.

- Signed informed consent from patients and/or their parents or legal guardians

Exclusion Criteria:

- Follicular lymphoma, mucosa-associated lymphoid tissue (MALT) and nodular marginal
zone

- PMLBL patients with CNS involvement

- Patients with congenital immunodeficiency, chromosomal breakage syndrome, prior organ
transplantation, previous malignancy of any type, or known positive HIV serology.

- Evidence of pregnancy or lactation period.

- There will be no exclusion criteria based on organ function.

- Past or current anti-cancer treatment except corticosteroids during less than one
week.

- Tumor cell negative for CD20

- Prior exposure to rituximab.

- Severe active viral infection, especially hepatitis B.

- Hepatitis B carrier status history of hepatitis B virus (HBV) or positive serology.

- Participation in another investigational drug clinical trial.

- Patients who, for any reason, are not able to comply with the national legislation.