The term diffuse large B-cell lymphoma (DLBCL) covers a rather heterogeneous group of lymphomas that are all characterized by diffuse tissue infiltration by large B-lineage lymphoma cells. Those that are related to human immunodeficiency virus (HIV) infection are dealt with separately (see Chapter 15). There are uncommon sub types, including mediastinal (thymic) large B-cell lymphoma, primary effusion-associated lymphoma and intravascular B-cell lymphoma. The disease can be primarily nodal or extra-nodal and can occur de novo or represent transformation of a lower grade non-Hodgkin's lymphoma, of nodular lymphocyte predominant Hodgkin's disease or of chronic lymphocytic leukaemia (known as Richter's syndrome).
Patients may present with localized or generalized lymphadenopathy (Figure 14.1) or with extra-nodal disease at a great variety of sites. In advanced disease there may be hepatomegaly, splenomegaly and involvement of central nervous system 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)  and intravascular B-cell lymphoma with multiorgan symptoms .
Clinical photograph showing cervical lymphadenopathy in a patient with diffuse large B-cell lymphoma (T-cell rich B-cell lymphoma).
Pre-treatment chest radiograph in a patient with mediastinal (thymic) large B-cell lymphoma.
Post-treatment chest radiograph in a patient with mediastinal (thymic) large B-cell lymphoma (same patient as Figure 14.2).
CT scan in another patient with mediastinal (thymic) large B-cell lymphoma.
CT scan in a patient with mediastinal (thymic) large B-cell lymphoma (same patient as Figure 14.4).
Haematological and pathological features
In the minority of patients with peripheral blood involvement, the lymphoma cells have a diameter that exceeds that of three erythrocytes (Figure 14.6). They are usually pleomorphic, and may have large nucleoli and irregular or cleft nuclei  (Figure 14.7). Sometimes cytoplasmic basophilia is prominent and a Golgi zone may be apparent.
Peripheral blood film showing large lymphoma cells with prominent nucleoli. Romanowsky stain, x 100 objective.
Ultrastructural examination showing pleomorphic large lymphoma cells, some with irregular nuclei and some with large nucleoli. Lead nitrate and uranyl acetate stain.