Burkitt lymphoma

Burkitt lymphoma occurs in two major forms, defined as endemic and sporadic. Endemic Burkitt is found primarily in Africa and typically presents in the jaw, orbit or paraspinal region, and is strongly associated with Epstein-Barr virus (EBV).

In other endemic regions however, it is relatively common for Burkitt lymphoma to present in the small intestine, usually involving the ileum, with preferential localization to the ileocaecal region {792}. In parts of the Middle East, primary gastrointestinal Burkitt lymphoma is a common disease of children. Sporadic or non-endemic Burkitt lymphoma is a rare disease, not associated with EBV infection, that frequently presents as primary intestinal lymphoma. Burkitt lymphoma is also seen in the setting of HIV infection when it often involves the gastrointestinal tract {236}. The histology in all cases is identical and is characterized by a diffuse infiltrate of medium-sized cells with round to oval nuclear outlines, 2-5 small but distinct nucleoli and a small amount of intensely basophilic cytoplasm. Numerous mitotic figures and apoptotic cells are present. The prominent starry-sky appearance is caused by benign phagocytic histiocytes engulfing the nuclear debris resulting from apoptosis. Thin sections often show

Fig. 4.20 Burkitt lymphoma. A Large ileocecal mass. B Starry-sky effect due to phagocytic histiocytes.

an unusual finding for lymphomas, whereby the cytoplasmic borders of individual cells 'square-off' against each other.

Burkitt lymphoma may rarely demonstrate a true follicular architecture, consistent with the proposed germinal center histogenesis of this neoplasm. It is a mature B-cell lymphoma and the neoplastic cells express pan-B-cell antigens

Fig. 4.21 Follicular lymphoma of terminal ileum.

CD19, CD20, CD22, and CD79a. In approximately 60-80% of cases, the neo-plastic cells co-express CD10, but fail to express CD5 or CD23. Surface immuno-globulin expression is moderately intense and is nearly always IgM with either kappa or lambda light chain restriction. The growth fraction, as assessed by Ki-67 or the paraffin equivalent MIB-1, is typically in excess of 90% of tumour cells. Burkitt lymphoma cells uniformly fail to express bcl-2.

Burkitt-like lymphoma

This group of atypical Burkitt lymphomas appears to represent a morphological overlap between Burkitt lymphoma and diffuse large B-cell lymphoma. The overall cell size is similar to Burkitt, but with greater pleomorphism {827}. These cases lack the typical monomorphic appearance of Burkitt lymphoma and demonstrate slight variation in both cell size and shape. The cells may have multiple nucleoli as in Burkitt lymphoma or a single distinct nucleolus. A starry-sky pattern may be evident and the mitotic rate is usually significantly increased. These lymphomas have a predilection for the gastrointestinal tract of adults, and also occur in the setting of HIV infection.

Other B-cell lymphomas

Any subtype of B-cell lymphoma can present as a primary small intestinal lymphoma, including those thought to arise from peripheral lymph node equivalents. De novo diffuse large B-cell lymphomas are the commonest lymphomas in the small bowel, and may develop from low-grade MALT lymphomas. Indolent lymphomas such as small lym-phocytic lymphoma, lymphoplasmacytic lymphoma and follicular lymphoma (cen-troblastic/centrocytic) can present as primary small intestinal disease. The latter subtype can occasionally produce the clinico-pathological entity of multiple lymphomatous polyposis, but can usually be distinguished from MCL by immu-nophenotypic and molecular genetic analysis {1034}.

Lymphoblastic lymphoma may underlie small intestinal lymphoma and frequently produces a mass in the ileocaecal region. Characteristic nuclear features and the expression of terminal nucleotidyl transferase may aid in establishing the diagnosis.

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