This is a retrospective, multicenter study focused on patients with a known diagnosis of PMLBCL which experienced a CNS relapse during the course of their disease to obtain information about the clinical characteristics, the management at diagnosis and at each relapses , and the outcome of these cases. The aim of the study is to put together the large International series on CNS+ PMLBCL data, coming from 6 different countries , on clinical factors, anti-lymphoma therapy administered alone or concomitant with CNS prophylaxis , the information about the site of re biopsy when available , the dose intensity of lymphoma therapy received at relapse and the outcome of patients.

Both patients treated in routine practice or within clinical trials will be considered. Moreover to better characterized the pathological features of this rare entity a central pathological review of the initial diagnosis and when available of for histological confirmed relapse will be considered.

Inclusion Criteria:

• Histologically confirmed diagnosis of Primary Mediastinal Large B Cell Lymphoma (PMLBCL) according WHO Classification
• Had a recurrence/progression with Central Nervous System (CNS) involvement
• Availability of details on clinical presentation, treatment details and outcome
• Availability of details on pathological data for central review
• Age ≥18 years

Exclusion Criteria

• Patients with CNS lymphoma other than PMLBCL subtype

Patients whose diagnosis met the histological criteria of PMLBL according WHO classification with a diagnosis of CNS involvement at relapse/progression.

Patients eligible to the study will be retrospectively identified by the site researches by interrogating the local site sources.

Availability of local pathological report at time of diagnosis and restaging will be considered for eligibility.