Non-Hodgkin lymphoma (NHL) is a heterogeneous group of disorders with varied clinical presentations. Primary extranodal NHL refers to initial disease involvement in any organ or tissue other than lymph nodes or the spleen. 

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All histologic subtypes of nodal lymphomas can arise extranodally but over 90% of cases are due to diffuse large B-cell lymphoma and mucosa-associated lymphoid tissue (MALT).1

Diffuse large B-cell lymphoma (DLBCL) represents approximately 30% of all lymphomas and is the most common lymphoma subtype worldwide.2 Chronic immunosuppression remains a significant risk factor underlying the development of both nodal and extranodal DLBCL.3

Multiple sclerosis (MS) is an inflammatory demyelinating disorder of the central nervous system (CNS). Monoclonal antibody-based treatment offers new therapeutic options for the management of MS. Natalizumab is a humanized recombinant monoclonal antibody that binds to the α4 subunit of the α4 β1 integrin (VLA-4) and interferes with the migration of leukocytes into the CNS.4

Initially approved for the treatment of relapsing forms of MS in 2005, natalizumab was voluntarily withdrawn from the market after two patients were diagnosed with progressive multifocal leukoencephalopathy (PML).

In 2006, natalizumab was reapproved with use in the United States restricted to highly active relapsing-remitting MS and patients not responding to or tolerating first-line therapy.

Natalizumab-induced impairment of immune surveillance in the CNS is thought to be one possible explanation for the increased incidence of PML and was implicated as a possible causative factor contributing to primary central nervous system lymphoma (PCNSL) after natalizumab use.5

Additional effects of natalizumab on the function and differentiation of immune cells including B lymphocytes may underlie a possible causal relationship in the development of extranodal DLBCL in patients receiving this medication.