Cbcl And Bcell Pseudolymphoma

Lymphoid cells of B-cell lineage express CD20 in most cases. CD19, CD22, and CD79a are also useful to verify the B-cell type. Follicular structures can be easily demonstrated by the presence of CD21-positive follicular dendritic cells (FDC) forming networks engulfing germinal center cells such as centroblasts and centro-cytes. CD138 antigen is useful for identification of plasma cell differentiation. Immu-nophenotypic features of mature B-cell neoplasms are summarized in Table 4. Often, a relatively high number of reactive small T-lymphocytes can be found in CBCL. One of the most vexing problems in dermatopathology is differentiation of B-cell pseudolymphoma (B-PSL) from a low grade malignant B-cell lymphoma. Apart from clinical and histologic features, the presence of irregularly structured- networks of CD21+ FDC, the monoclonal expression of immunoglobulin light chains kappa and lambda, and the coexpression of CD20 and CD43 on tumor cells argues for the presence of CBCL, but does not absolutely exclude B-PSL (Fig. 1A and B). Immu-nohistochemical markers applied for differentiation of follicular center cell lymphoma from pseudolymphoma are listed in Table 5 .

Although the clinical manifestations and cellular composition are the most important factors in determining the classification of CBCL, IHC is very useful in identifying subtypes. Whereas tumor cells express CD20 in follicle center cell lymphoma (FCCL) and marginal zone lymphoma, they are negative for CD20 in both plasmacytoma and pre-B lymphoblastic lymphoma, which is also positive for TdT. Bcl-2 is often found in nodal FCCL, but only in a minority cases of primary cutaneous FCCL and in a subset of diffuse large B-cell lymphomas (7). CD5 can be found in infiltrates of B-cell chronic lymphocytic leukemia (B-CLL), but not in primary CBCL with the exception for rare cases of diffuse large B-cell lymphoma (DLBCL). KiMlp with its characteristic granular staining pattern is exhibited by monocytoid B-cells in MZL. Occasionally, CD30+ blasts resembling centroblasts are present in the germinal centers of FCCL and 172L. Although IHC provides useful information, the final diagnosis in CBCL must also consider all clinical, histolo-gic, phenotypic, and genotypic features and not rely on one single criterion.

Table 4 Mature B-Cell Neoplasms Involving the Skin

Tumor

CD20, CD79

CD5, CD 10, CD23,

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