High magnification showing a uniform population of small to medium sized lymphocytes that make up the expanded white pulp. They have round to slightly irregular nuclear contours, condensed chromatin, and inconspicuous nucleoli. Mitotic activity is not increased. Immunophenotypically, the CLL/SLL cells are light chain restricted mature B-cells that coexpress CD23 and show aberrant expression of T-cell marker CD5. They are positive for CD19, CD20 (dim), and CD11c (dim). They are negative for CD10, FMC-7, CD38, and CD79b.