BCL-2 immunostaining of neoplastic lymphoid tissue.

(A) In a low-grade MALT lymphoma, BCL-2 is expressed by the diffuse neoplastic infiltrate lying beneath the intestinal mucosa (Muc). BCL-2 is absent from reactive germinal centers (asterisks) in the tumor and from areas of high-grade transformation. The high-power view (bottom) shows the border between a low-grade area and a high-grade area. The arrows indicate large BCL-2–negative neoplastic cells. Original magnification top, × 200; bottom, × 800. (B) A pseudonegative follicular lymphoma in which the cells in a neoplastic follicle (Foll) lack BCL-2. However, a higher-power examination of the boxed area (center and bottom) shows that many of the BCL-2–positive small interfollicular cells (arrows) are neoplastic centrocytes (small cleaved cells). (Alkaline phosphatase–antialkaline phosphatase [APAAP] technique in paraffin sections; reproduced with permission from American Journal of Pathology47.) Original magnification top, × 250; center, × 400; bottom, × 800.