Low power images at the top demonstrate multiple closely packed monotonous follicular structures which do not resemble reactive follicles.  At higher power inside these follicles (bottom 2 images), numerous large centroblastic cells are apparent.  Scattered small lymphocytes are present for comparison.Scattered mitoses are also easily visualized in the image on the bottom left.

CD20 immunostain highlights multiple closely packed serpiginous coalescent follicles.  All neoplastic follicles are positive for CD20. The image on the right demonstrates extra follicular extension of lymphoma cells seen as clusters of CD20 positive cells.

The germinal center markers, CD10 (top left and right) and BCL6 (bottom left and right) are both positive within the neoplastic follicles. The image on the top right shows extra follicular extension of CD10 positive lymphoma cells.  Often, the extra follicular component demonstrates down-regulation of CD10 and or BCL6.

The neoplastic follicles are also positive for BCL-2 at low power and high-power.  Often, BCL-2 may be negative in high-grade follicular lymphomas

MYC immunostain is positive in cells at the periphery of the neoplastic follicles.  The neoplastic follicles are strongly positive for Ki-67 with nearly 70% proliferative cells.

PD–L1 is negative and the lymphoma cells but highlights positive histiocytes with membrane staining present within the neoplastic follicles and at the periphery of the neoplastic follicles.

Numerous CD21 positive follicular dendritic cell meshworks are present within the neoplastic follicles.  This stain is often used to assess for possible areas of transformation which frequently lack underlying CD21 positive meshworks.