FLIS. (A-B) H&E-stained (A) and BCL2-stained (B) sections of LN showing replacement of a germinal center by centrocytes with uniformly intense positivity for BCL2. The surrounding mantle cuff is intact and shows relatively weak BCL2 positivity. Original magnification ×200. (C-D) FLIS in an LN stained for BCL2 (C) and CD10 (D). The single involved follicle is strongly positive for BCL2 and CD10. Mantle zone B cells and T cells show less intense BCL2 positivity. Normal germinal centers are BCL2⁻ and only dimly CD10⁺. Original magnification ×40. (E-G) Several examples of FLIS patterns. (E-F) LNs with overall intact architecture but with the minority (E) or majority (F) of follicle centers involved by FLIS. Original magnification ×20. The individual follicles exhibit various degrees of involvement by FLIS cells (G), and a similar pattern is seen in a case from a patient who had a prior history of follicular lymphoma (H; case 23 in Table 3). Original magnification ×40.