Low-grade follicular lymphoma and small lymphocytic lymphoma show BMI-1^low/EZH2⁺ centroblasts associated with cycling cells.

(A-C, first row) IF on follicular lymphoma (Berard grade I/II) with BMI-1 (red fluorescence) and EZH2 (green fluorescence). BMI-1 expression is detectable in most centrocytes (A). Large, bright red cells are macrophages (MΦ). Weak but distinct BMI-1 expression is detectable in neoplastic centroblasts (dotted arrow in A), which are also EZH2 (B; arrow). This produces a yellow signal in C. (D-F, second row) IF for BMI-1 (red fluorescent signal) and EZH2 (green fluorescent signal) on lymphocytic lymphoma. BMI-1 expression is detectable in almost all tumor cells (D), and a limited number of cells are EZH2⁺ (E). These cells coexpress BMI-1, producing a weak yellow signal in panel F (overlay photographic exposure) similar to that in panel C. (G-I, third row) IF for Mib-1/Ki-67 (red fluorescence) and EZH2 (green fluorescence) on follicular lymphoma. (G) Mib1/Ki67⁺ cells. (H) EZH2⁺ cells (using a stronger Alexa fluorescent probe than the FITC probe in panel B). (I) Overlay photographic exposure showing overlap between EZH2 and Mib/Ki67. One representative example is shown. Lymphocytic lymphoma gave a comparable result (not shown). All photographs were taken with a 63× objective.