Follicular lymphoma is a B-cell neoplasm composed of germinal center B cells (centrocytes and centroblasts). It makes up about 20% of non-Hodgkin lymphoma in USA and Western Europe. Patients are usually asymptomatic (even when disease is disseminated) at presentation with an overall 10-year survival of up to 80%. It is characterized by closely packed neoplastic follicles, uniform in size and shape. The neoplastic follicles contain variable amounts of centrocytes and large centroblasts. Grading is based on the number of centroblasts per high power field and is associated with prognostic and therapeutic significance.

The needle core biopsy shows nodular proliferation of mostly small cleaved atypical lymphoid cells (centrocytes) and less numerous large non-cleaved atypical lymphoid cells (centroblasts, <15/HPF). The atypical lymphoid cells are positive for CD20, PAX5, BCL6, CD10, BCL2, and are negative for CD5 and BCL1. CD3 and CD5 are positive in the surrounding T cells. CD21 and CD23 (not shown) are positive in follicular dendritic cell meshworks, some of which are expanded. MIB1 stain shows a proliferation index of 10-20%. The morphology and immunohistochemical profile are in keeping with follicular lymphoma, grade 1-2.

See Related Content for associated stains in this case.