Immunostains of MIB-1 (A), Bcl-2 (B), CD10 (C), and Bcl-6 (D) in a case of classic Burkitt lymphoma. Note that all cells are proliferating as defined by positive MIB-1 staining, except the phagocytic histiocytes in the section. CD10 is strongly expressed by the malignant cells, and Bcl-2 is negative. Note several small, reactive lymphocytes in the section staining positively for Bcl-2 that serve as an internal control. Bcl-6 staining (D) shows strong nuclear expression.