Classification of non-Hodgkin's lymphomas

Non-Hodgkin's lymphomas are tumors from lymphoid cells of different histogenetic affiliation and degree of differentiation. The group includes more than 25 diseases. Differences in the biology of non-Hodgkin's lymphomas are due to the characteristics of the cells that form them. It is the constituent cells that determine the clinical picture, the sensitivity to therapy and the long-term prognosis. For most lymphomas, specific nonrandom chromosomal translocations and rearrangements of receptors are known, which are key in pathogenesis.

According to the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissue in 1999, non-Hodgkin's lymphoma types are determined on the basis of morphology, immunophenotype, genetic characteristics of tumor cells and clinical presentation of the disease.

The classification is based on the proposals of the Lymphoma Research Group, which combined the main positions of the Kiel (mostly European) classification and the so-called Workplace formulation used in the US and Canada.

Non-Hodgkin's lymphomas are divided into main groups, depending on whether they belong to the T- or B-lines of lymphopoiesis. Further detailing is determined by the degree of differentiation of tumor cells, the localization and histological structure of the tumor, the features of the course of the disease.

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The main types of non-Hodgkin's lymphomas in children

In children, the spectrum of histological variants of non-Hodgkin's lymphomas is relatively narrow. It is proved that all species are generalized already at the earliest stages of presentation, and in 95% of cases - highly malignant. Tumors develop mainly from the precursor cells of T- and B-lymphocytes, have a diffuse histological structure. Based on the morphological and histological characteristics of children's non-Hodgkin's lymphomas can be divided into three main groups - Burkitt's lymphomas (and berkitt-like), lymphoblastic and large-celled. This classification is practically consistent with the sections of the Work Statement and is convenient from the point of view of therapy (the protocols used in Russia for treatment of children's non-Hodgkin's lymphomas developed by the BFM group suggest a similar division into three main therapeutic groups). However, this approach was the reason for the error in determining the tactics of treating children with large cell lymphomas in the early years of using these protocols in Russia, when patients received protocol treatment for anaplastic large-cell lymphoma, whereas variants of diffuse large-cell lymphomas from B-lymphocyte progenitors require more aggressive therapy. Currently, diagnosis of non-Hodgkin's lymphomas should be carried out in accordance with the WHO international protocol.

For children under the age of 15, the following histological variants of non-Hodgkin's lymphomas are typical.

• Lymphoblastic lymphomas, in the overwhelming majority of cases consisting of T-cells, rarely (about 10%) of B-progenitor cells;
• Diffuse B-cell, 70% of which is Burkitt's lymphoma and berkitt-like with a B-immunophenotype. The mandatory elements of which are the presence of surface IgM (or light chains), a high proliferative index of Ki 67 (up to 100% of cells), the presence of C-mic rearrangement, specific translocations 8; 14, 8; 22 and 2, 8.
• Large cell lymphomas (15-20% of children's lymphomas). Belonging mainly to the B-line of lymphopoiesis.

Among large cell lymphomas, several variants are distinguished, which does not affect the choice of treatment tactics. One-third of children's large cell lymphomas are anaplastic large cell lymphoma with T-immunophenotype (very rarely B-cell or from cells that carry neither T- nor B-cell markers), an activating marker CD30 and a specific chromosomal translocation between sites and chromosomes 2 and 5 - t (2; 5) - with the participation of the kinase gene of anaplastic lymphoma (alk).

Rarely, no more than 5% of patients diagnose other variants of non-Hodgkin's lymphomas - peripheral large cell, follicular, true histiocytic lymphoma, unclassifiable.

Very high proliferative potential causes rapid growth of children's lymphomas.