Burkitt lymphoma in individuals infected by HIV. Burkitt lymphoma with plasmacytoid differentiation; phenotypically, the tumor cells express B-cell antigens including CD20, CD10, and BCL6 and are consistently negative for BCL2. The proliferation index is very high, approximately 100%. (A) A homogeneous proliferation of medium-sized tumor cells displays a cohesive pattern. Tumor cells show round nuclei, multiple nucleoli, and small basophylic cytoplasm. Immunoblastic-like tumor cells (in the red circle) with larger nucleoli are also seen. Tumor cells typically express CD10 with membranous staining pattern and BCL6 with nuclear staining pattern. (B) Burkitt lymphoma involving capsular and extranodal tissues (arrows; i) and a hyperplastic lymphoid follicle within a reactive hyperplastic lymph node (ii). The extranodal pattern of tumor infiltration is confirmed by Ki-67 staining. H&E, hematoxylin-eosin stain; CD10, BCL6, and Ki-67 immunohistochemistry, hematoxylin counterstain. Original magnification, ×200. Images were taken using a Nikon Eclipse 80i microscope with a Plan Fluor 20×/0.75 objective and Nikon digital sight DS-Fi1 camera equipped with control unit-DS-L2. Images were processed using Adobe Photoshop CS2 V9.0.