Introduction A variety of lymphomas can involve the central nervous system (CNS), at different phases of their evolution, in both immunocompetent and immunocompromised individuals. They represent a heterogeneous group of malignancies, with variable clinical and behavioral characteristics, requiring different therapeutic approaches. In this chapter, the therapeutic management of these malignancies will be analyzed separately in three main entities: primary CNS lymphomas (PCNSL), secondary CNS lymphomas (SCNSL) and other, less common, forms of CNS lymphomas. The vast majority of CNS lymphomas are diffuse large B-cell lymphomas (DLBCL) that share the morphological and immunophenotypic characteristics similar to those of DLBCLs encountered elsewhere. They may show a perivascular growth pattern. The perivascular infiltrate is associated with increased reticulin fibres and the periphery of areas of involvement frequently shows astrocyte gliosis. Many immunocompromised patients show features similar to Burkitt's lymphoma, while others show a more immunoblastic morphology. Rare cases of small lymphocytic, lymphoplasmacytic and T-cell lymphoma similar to those seen in tissue outside the CNS have been described. Secondary involvement by lymphoma originating elsewhere is also encountered. Immunophenotypically CNS lymphomas recapitulate the staining pattern of similar lymphomas encountered outside the CNS. The DLBCLs are positive for CD20 and CD79a with expression of bcl-2 protein. A proportion express CD10 and bcl-6, but they are usually negative for CD5 and CD23. Large B-cell lymphomas in immunocompromised patients frequently contain Epstein–Barr virus (EBV).
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