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Immunophenotype: The neoplastic cells in cutaneous follicle center lymphoma consistently express B-cell markers (CD19, CD20, CD22, CD79a, PAX5), BCL6, and variably express CD10 (pos in follicular pattern; neg in diffuse pattern). They are negative for CD5, Cyclin D1, CD43, BCL2 (or only weakly +), immunoglobulins, IRF4/MUM1 and FOXP1. The neoplastic germinal centers have lower Ki-67 proliferation index than reactive germinal centers and do not show polarization.
If there is diffuse strong staining for BCL2, BCL6, and CD10, it should raise the concern for a systemic/nodal follicular lymphoma with secondary skin involvement.
Early lesions show prominent follicular dendritic cell meshwork with CD21 and CD35 immunostains. Cases with diffuse growth pattern usually lack this feature.
If there is diffuse strong staining for BCL2, BCL6, and CD10, it should raise the concern for a systemic/nodal follicular lymphoma with secondary skin involvement.
Early lesions show prominent follicular dendritic cell meshwork with CD21 and CD35 immunostains. Cases with diffuse growth pattern usually lack this feature.