FISH of FLIS. (Top panels) Two FLIS follicles stained for BCL2. FISH was examined in follicular and interfollicular areas. Within the FLIS follicle, a cell shows a split red and green signal, indicating a BCL2 break (top right). (Bottom panels) Cells with split signals are seen only in involved follicle, to right of dotted line, and not in uninvolved areas, to left of dotted line. The involved follicle is shown at higher power (bottom right).