Both classifications, Kiel and IWF, have their advantages and disadvantages, страница 2

Both classifications, Kiel and IWF, have their advantages and disadvantages. The Kiel classification has the advantages of

a) incorporating morphology and immunology and distinguishing categories of B and T-cell lymphomas;

b) separating lymphomas into low and high grade of malignancy;

c) subdividing T-cell malignant lymphomas into several groups;

d) including peculiar categories of lymphomas such as marginal zone/B-monocytoid cell and large cell (Ki-1+) anaplastic lymphomas. The only disadvantage of the Kiel classification is that it designates as low-grade malignant lymphomas some entities like centrocytic (mantle cell), AILD-like, T-zone and peripheral pleomorphic small T-cell lymphomas, although their course is either relatively aggressive or unpredictable. The IWF classification, on the other hand, is purely descriptive and does not distinguish between B and T-cell entities. The T-cell distinction is completely absent. In addition to high and low grade of malignancy, the IWF distinguishes a third, intermediate grade. This distinction seems unnecessary as most of the lymphomas belonging to this latter group behave and are treated like those of high-grade malignancy [30,31], while some of them should be placed in the low-grade category. In the present work the Kiel classification is used primarily, and an attempt is made to correlate it with the IWF. Some peculiar lymphoma entities of histopathogenic, prognostic or differential diagnostic importance which are difficult to incorporate into either of the above classifications are described separately.

Low Grade Malignant Lymphomas

Low-grade malignant lymphomas are histologically characterized by the presence of small or medium-sized lymphoid cells. Sometimes they are mixed with limited numbers of larger blastic cells, for example in the so-called centroblastic-centrocytic malignant lymphomas.

Lymphocytic Lymphoma

The malignant lymphomas included in this group consist mainly of lymphocytes or their forms of prolymphocytes and hairy cells. They belong more frequently to the B than to the T-cell lineage.

Chronic lymphocytic leukemia of B-cell type (B-CLL)

This is characterized by infiltration with B lymphocytes that do not show any transformation to Ig-secretory cells such as lymphoplasmacytoid and plasmacytic cells. This interruption of maturation could be attributed partly to defective CD4+ helper T cells and partly to an increased activity of CD8+ suppressor T cells . Immunohistochemically  the neoplastic lymphocytes express the B-cell antigens CD20, CD22 and CD23, are either kappa or lambda monoclonal and show SIg of the IgM class, frequently together with IgD. However, not rarely B-CLL lymphocytes especially after micro-wave retrieval may show some intracytoplasmic Ig-positivity. This fact, in conjunction with the positivity for CDS antigen, raises the possibility of B-CLL and lymphoplasmacytoid immunocytoma being variants of the same entity [34]. They seem to be histogenetically related to CDS-positive lymphocytes of the primary follicle or the follicular mantle zone [35]. B-CLL does not occur in subjects under 20 years of age. It shows generalized lymphadenopathy and usually a leukemia picture with bone marrow infiltration. According to Rappaport's group cases of lymphocytic lymphoma [32,36] may exist without any synchronous or metachronous leukemia picture. Effacement of the normal lymph node structure is observed histologically due to diffuse infiltration with maturing lymphocytes [34,36-38]. Among these larger lymphocytes, the prolymphocytes [39], are found with less dense chromatin and prominent nucleoli as well as large cells, the paraim-munoblasts with basophilic cytoplasm, oval nuclei and central, prominent nucleoli. They are sometimes dispersively distributed but more frequently form clusters (pseudofollicular foci or proliferation centers, Fig. 1). Mitoses and positivity for the proliferation antigen Ki-67 are present only in prolymphocytes and paraimmunoblasts where also most of the p53 oncoprotein positivity is expressed [40]. The greater the proliferation centers, the more tumors is the appearance of the lymph nodes. About 4% of the cases eventually develop into true, high-grade malignant lymphoma, usually immunoblastic (Richter's syndrome) [41]. In some cases a development of giant cells similar to Hodgkin and Sternberg-Reed cells superimposes the B-CLL morphology. Such cells are positive for Epstein-Barr virus elements (LMP, EBER) and Ki-1 (CD30) antigen, a fact which renders possible a relationship of such cases with Hodgkin's disease [42]. Patients usually survive for many years without any substantial therapy. The extent of bone marrow infiltrates and their way of distribution are of particular importance [43]. More favorable prognosis have the cases with nodular patterns (Fig. 2) while cases with diffuse distribution survive less. The prognosis also seems to depend on the size and number of proliferation centers in the lymph nodes [44].