Mantle Cell Lymphoma

General: Mantle cell lymphoma (MCL) represents approximately 6% of lymphomas.1 It generally presents in middle-aged to older adults with a median age of approximately 60 and a male predominance. Stage 3 or 4 involvement is common at presentation and bone marrow involvement is seen in more than half the patients at presentation. Although nodal disease is most common, primarily extranodal disease involving Waldeyer's ring or the gastrointestinal tract does occur.5

Pathology: Nodular, mantle zone, and diffuse architectural patterns of infiltration can occur. In the mantle zone pattern, the lymphomatous infiltrate surrounds reactive germinal centers. In the nodular pattern, the infiltrate replaces normal follicles. The diffuse pattern is most common. The infiltrate is very monotonous and is composed of small lymphocytes with slightly irregular nuclei, condensed chromatin, and inconspicuous cytoplasm (Figure 52.4). Mitotic

Figure 52.4 MCL, low magnification shows a diffuse infiltrate of small lymphocytes. Inset (upper right) shows the high magnification appearance with an epithelioid histiocyte in the center. The lower inset show cyclin D1 expression

figures, unusual in other low-grade B-cell lymphomas, are commonly seen in MCL. Epithelioid histiocytes are frequently admixed in the infiltrate, imparting a "mottled" look at low to intermediate magnification.

The blastoid variant is an aggressive variant of MCL and is characterized histologically by intermediate-sized cells. A fine blast-like chromatin can be seen in some cases resembling lymphoblastic lymphoma. Other cases have a more pleomorphic appearance and more closely resemble large cell lymphoma.6 Mitotic figures (>20/10 hpf) are seen and associated with a poor prognosis.5

Immunophenotype: The characteristic immunopheno-type of MCL is CD5 + , CD10-, CD19+, CD20+(bright), CD23-, FMC7 + , surface Ig light chain restricted, and cyclin D1 + .7

Molecular genetics: Expression of cyclin D1 is seen in the vast majority of cases and is a consequence of the t(11;14)(q13;q32) that helps define this lymphoma. Only rare cases of MCL may lack this translocation.8 This translocation can be detected by standard cytoge-netics or FISH. PCR assays exist but because of the variability in breakpoints these are not as widely used in clinical laboratories as FISH. Blastoid mantle cell lymphomas have characteristic (although not specific) additional genetic abnormalities such as TP53 mutation, deletion of P16, deletion of P21, and tetraploidy.9-11

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