Lymphoplasmacytic Lymphoma

General: Lymphoplasmacytic lymphoma (LPL) is an uncommon lymphoma (1% of lymphomas) that presents equally in men and women. The median age at diagnosis is 63 years.1 A subset of patients, approximately 25%, present clinically with Waldenstrom macroglobulinemia. The overall survival at 5 years is 59%.1

Figure 52.11 Nodal marginal zone B-cell lymphoma. At high magnification, the cytologic features of the lymphoma cells surrounding the follicle in Figure 10
Figure 52.12 Lymphoplasmacytic lymphoma consisting of a diffuse infiltrate of small lymphocytes and plasma cells

Pathology: The morphologic features of LPL are variable. Cytologically, the lymphoma is composed of small lymphocytes with plasmacytoid features and plasma cells that are part of the neoplasm. Dutcher bodies (intranuclear cytoplasmic intrusions) can be seen. Recently, three morphologic patterns have been described. In one, there are open sinuses with small follicles. In the second, there are hyperplastic germinal centers, and in the third there is diffuse effacement of the lymph node (Figure 52.12). Epithelioid histiocytes are commonly seen.

Immunophenotype: The lymphoma cells express CD 19 and CD20 with surface immunoglobulin. Cytoplasmic immunoglobulin is expressed in the plas-macytic cells and heavy chain is usually IgM, although other can be seen uncommonly. Presence of CD5 should prompt consideration of CLL/SLL.

Molecular genetics: Relatively little is known regarding the molecular genetics of LPL. Immunoglobulin genes are clonally rearranged. Initials studies have suggested a t(9;14)(p13;q32) translocation; however, recent studies suggest this is not a common occur-rence.52

Occasional cases are composed of large centrocytes with open chromatin. Mitotic figures are variably prominent. In some case, partial involvement of the lymph node can be seen. Rare cases will involve inter-follicular areas.

Extranodal DLBLCs appear similar to nodal cases. Some may represent transformation of MALT lymphomas. A variant of DLBLC, primary mediastinal DLBCL, typically has lobulated cells and sclerosis. Another variant, intravascular DLBCL involves vessels only.

Immunophenotype: The vast majority of DLBCLs express pan-B-cell antigens such as CD19 and CD20. Surface immunoglobulin is expressed in most cases but may be lacking in some.54 Expression of bcl-2 and high Ki-67 index have been associated with poor prognosis in DLBCL.5556 Bcl-6 expression has been suggested to be indicative of a more favorable outcome.57 Recent expression array studies have shown that phenotyping with CD10, Bcl-6, and MUM-1 can help identify the germinal center type of DLBLC (Figure 52.13).58

Molecular genetics: Rearranged B-cell receptor genes are present. Recurrent genetic abnormalities can be found. For example, the t(14;18)(q21;q32), characteristic of FL, can be seen in approximately 20% of DLBLC.59 BCL6 rearrangements are also common and can be found in approximately 30% of cases.60 Much progress has been made in understanding gene expression patterns in DLBCL by using microarrays.61-63 These studies have allowed distinction of prognostic subgroups within DLBCL, which are independent of the International Prognostic Index. Germinal centerlike DLBCL (having expression patterns similar to germinal center B-cells) appear to have a favorable prognosis compared to the activated B-cell like DLBCL (having expression patterns similar to activated B-cells). Distillation of this complex data to practical clinical laboratory assays is beginning. Genetic expression models

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