Molecular and virologic characteristics of lymphoid malignancies in children with AIDS

Imaging of pediatric lymphomas

Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL) represent 10% to 15% of all malignancies occurring in children younger than 20 years of age. Advances in cross-sectional imaging and the availability of positron emission tomography (PET) and PET-CT have had a major impact on imaging and management of pediatric patients. This article reviews the clinical features of lymphoma, focusing on the spectrum of imaging findings seen in diagnosis, staging, and follow-up of HL and NHL. Pediatric NHL has four major histologic subtypes: Burkitt lymphoma, diffuse large B-cell lymphoma, anaplastic large cell lymphoma, and lymphoblastic lymphoma. The most important subtype of HL is nodular sclerosis.

Possible close analogy between HIV and EBV infection and, respectively, induced lymphomas

Within a system that operatively allows a progressive infection of T-lymphocytes by human immunodeficiency virus (HIV) in a manner that also entails depletion of the T-helper subset with directly resulting severe immunodeficiency, there might also be implicated a form of modulation of effects conducive to neoplastic transformation based on peculiar consequences of lesions induced by HIV integration within the cell genome. It might, in addition, be valid to consider Epstein Barr virus (EBV) as a cause of both B-lymphocyte infection and also of the creation of a whole population of atypical T-lymphocytes as seen in infectious mononucleosis, to constitute a close parallel analogy to HIV; in this manner it might be suggestive also of a series of analogous reactive lymphocytic changes also in AIDS; such a phenomenon might perhaps help account for the emergence in some AIDS patients of a primary Central Nervous System Lymphoma that is virtually always of B-cell derivation, analogous to Burkitt's lymphoma that is also of B-cell origin. In addition, the occurrence of T-cell rich B-cell lymphoma would appear perhaps to constitute a series of phenomena that intricately implicate both B-lymphocyte and T-lymphocyte participation in the genesis even of lymphomatous states as a category.

[Muscle tumor in a girl with HIV infection: extranodal non-Hodgkin's lymphoma]

Non-Hodgkin's lymphomas are the most common cancers in children with human immunodeficiency virus (HIV) infection. Extranodal disease is the most common form of clinical presentation. Treatment with aggressive chemotherapy and highly active antiretroviral therapy has improved the prognosis of these children. We present a 10-year-old severely immunocompromised girl with HIV infection and non-Hodgkin's lymphoma manifested by a muscle mass.

Emerging pathways in the development of AIDS-related lymphomas

The clinicopathological range of AIDS-related non-Hodgkin lymphomas (NHLs) includes systemic lymphomas, primary central-nervous-system lymphomas, primary effusion lymphoma, and plasmablastic lymphoma of the oral cavity. Most AIDS-related NHLs belong to one of three categories of high-grade B-cell lymphomas: Burkitt's lymphoma, centroblastic lymphoma, and immunoblastic lymphoma. The pathological heterogeneity of AIDS-related NHL reflects the heterogeneity of their associated molecular lesions. In AIDS-related Burkitt's lymphoma, the molecular lesions involve activation of c-MYC, inactivation of p53, and infection with Epstein-Barr virus (EBV). AIDS-related immunoblastic lymphomas infected with EBV are characterised by frequent expression of latent membrane protein 1-an EBV oncoprotein. The biological heterogeneity of AIDS-related NHLs is highlighted by their histogenetic differences; AIDS-related NHLs are related to distinct B-cell subgroups (eg, germinal-centre or post-germinal-centre B cells). The phenotypic pattern of AIDS-related Burkitt's lymphomas and systemic AIDS-related centroblastic lymphomas closely reflects that of B cells in germinal centres. Conversely, the phenotype of AIDS-related immunoblastic lymphomas and AIDS-related primary effusion lymphomas reflects post-germinal-centre B cells in all cases. Despite their clinicopathological, genetic, and phenotypic heterogeneity, most lymphomas in patients with AIDS carry somatic mutations of immunoglobulin and BCL-6 genes. However, the somatic hypermutation mechanism functions aberrantly in a significant proportion of AIDS-related NHLs, causing the mutation of many genes, and possibly favouring chromosomal translocation, which may be a powerful contributor to malignant transformation. New molecular and virological evidence of such pathways and a greater knowledge of other biological features of AIDS-related NHLs may lead to new targets for pathogenetically and biologically oriented therapies.