Recommended positive control: Lymphoid tissues
Staining pattern: Membrane
Reacitivity in normal cells: B lymphocytes. Plasma cells are negative.
One of the most reliable B-cell markers.
In reactive lymphoid tissues, CD20 positive cells should show a pattern “nodular aggregates and scattered cells in interfollicular area”.
In B-cell lymphomas, typically show “diffusely positive”.
Left: Reactive hyperplasia
Right: Follicular lymphoma
Peripheral areas of normal lymphoid tissues tend to be diffuse distribution of B-cells.
Some B-lineage lymphomas may show CD20-negative: B-LBL, plasma cell neoplasms, some case of SLL/CLL, cases status post-rituxian therapy. In those cases, CD79a should be added.