Both classifications, Kiel and IWF, have their advantages and disadvantages, страница 6

Mycosis Fungoides and Sezary's Syndrome

These two types represent, together with T-CLL, the classic example of low-grade T-cell lymphomas, which all belong to the peripheral T-cell lymphomas. They derive from peripheral T lymphocytes [120], in contrast to T-lymphoblastic lymphomas which derive from central T cells of the thymic or prethymic stage. Mycosis fungoides primarily involves the skin. Lymph nodes and other organs are infiltrated in advanced stages. The T lymphocytes of MF show a cerebriform, gyroid nucleus (Lutzner cells). In most cases they belong to helper CD4-positive cells and only exceptionally they are CDS-positive. Some cases with expression of both phenotypes have been described [121]. Sometimes the functional stimulation of the neoplastic CD4-cell clone on reactive B lymphocytes induces B-cell clone expansion with monoclonal plasma cells on the tissue level and a paraprotein in blood serum [122]. Skin lesions exhibit 3 stages of development [123,124]. Firstly the premycotic stage, which histologically is easily confused with inflammatory lichenoid infiltrates. In such cases immunohistochemistry is of significant help since in reactive inflammatory cases intraepidermal and dermal cell infiltrates are of the same phenotype. In cases of neoplastic MF lesions a discrepancy in the phenotype expression between the two cell groups may be found because of neoplastic loss of some surface markers [123,125,126] which seems to occur exclusively in intraepidermal T cells [127]. The second, infiltrate stage is histologically diagnostic as it shows dense cell infiltration of the dermis and clear epidermotropism with the characteristic Pautrier's microabscesses. Among the dermal infiltrates there are numerous interdigitating reticulum cells with a simultaneous hyperplasia of Langerhans cells in the overlying epidermis. Both are characterized Immunohistochemically by their positivity for SIOO-protein and CD1-antigen . In the third, tumor stage the neoplastic infiltrates consist of larger transformed Lutzner cells and/or large immunoblastic cells in various numbers. The histological picture is compatible with any one of the various types of high-grade malignant peripheral T-cell lymphomas. T-immunoblastic cells and anaplastic large T-cell forms are usually positive for Ki-1 antigen. Sezary's syndrome can be regarded as the leukemia variety of mycosis fungoides. In both conditions bone marrow involvement is seldom seen and only in advanced stages. The lymph nodes initially show lesions typical of dermatopathic lymphadenopathy with prominent interdigitating reticulum cells in expanded T-cell areas. Neoplastic infiltration of lymph nodes, which occurs in later stages, is considered a bad prognostic sign [128]. It is marked by the infiltration of the T-zone areas by varying cumbers of atypical cerebriform cells. The infiltrates are denser and more monomorphic in cases of Sezary's syndrome while interdigitating cells are more prominent in cases of mycosis fungoides. The relatively high numbers of Ki-67-positive cells, as well as DNA flow cytometry findings and TCR rearrangement [129-130] facilitate the documentation of neoplastic lymph node infiltration.

T-zone Lymphoma

This is a rare lymphoma. It is the counterpart of the follicular centroblastic/centrocytic lymphoma [131], in the sense that in the early stages of growth the non-neoplastic germinal centers of the lymph node remain intact while the extrafollicular T-areas with the proliferating post-capillary venules represent the neoplastic sites. The nuclei of the neoplastic T lymphocytes are usually monomorphic and occasionally slightly pleomorphic. Their cytoplasm is scanty. However, some larger cells with clear cytoplasm or immunoblastic characteristics (T-immunoblasts) can also be found. Islands of plasmacytoid monocytes and occasional eosinophils and/or epithelioid cells may be observed. Immunohistochemically the neoplastic cells show a mature T-cell phenotype: CD22+> CD23+, CD5+ and mostly CD4+.