The term diffuse large B-cell lymphoma (DLBCL) covers a rather heterogeneous group of lymphomas that are all characterized by tissue infiltration by medium sized to large B-lineage lymphoma cells . There are uncommon variants and entities that have particular localizations, such as mediastinal (thymic) large B-cell lymphoma , primary effusion lymphoma , primary DLBCL of the central nervous system (CNS) , primary cutaneous DLBCL leg type , and others that have distinct pathological features, such as intravascular large B-cell lymphoma , plasmablastic lymphoma , T-cell/histiocyte-rich large B-cell lymphoma  and ALK-positive large B-cell lymphoma . Some of these variants and entities also have distinct biological and genetic abnormalities. The lymphomas that are related to human immunodeficiency virus (HIV) infection are dealt with separately (see Chapter 16). The present chapter will describe the large number of remaining cases that are not otherwise specified (NOS) and are designated DLBCL, NOS. Some of the distinct features of the above variants or entities will also be briefly described. DLBCL, NOS can be subdivided into germinal centre B-cell-like (GCB) and activated B-cell-like (ABC). The disease can be primarily nodal or extra-nodal and can occur de novo or represent transformation of a lower grade non-Hodgkin lymphoma such as follicular or marginal zone lymphoma, or of nodular lymphocyte predominant Hodgkin lymphoma or of chronic lymphocytic leukaemia (known as Richter’s syndrome).
DLBCL affects predominantly the elderly and is slightly more common in men. Patients may present with localized or generalized lymphadenopathy (Figure 14.1) or with extra-nodal disease at a great variety of sites, most frequently the gastrointestinal tract. In advanced disease, there may be hepatomegaly, splenomegaly and involvement of CNS or bone marrow, with or without circulating lymphoma cells. Mediastinal large B-cell lymphoma presents as a thymic mass (Figures 14.2, 14.3, 14.4, 14.5), primary effusion lymphoma with pleural or pericardial effusion or ascites (usually in an HIV-positive patient), intravascular B-cell lymphoma with multiorgan involvement, primary CNS lymphoma with involvement of this organ and primary cutaneous DLBCL, leg type with single or multiple skin lesions.
Clinical photograph showing cervical lymphadenopathy in a patient with diffuse large B-cell lymphoma (T-cell/histiocyte-rich B-cell lymphoma).
Pre-treatment chest radiograph of a patient with mediastinal (thymic) large B-cell lymphoma.
Post-treatment chest radiograph of a patient with mediastinal (thymic) large B-cell lymphoma (same patient as Figure 14.2).
Computed tomography (CT) scan in another patient with mediastinal (thymic) large B-cell lymphoma.