At low power, multiple discrete white pulp nodules are noted. On higher power these nodules are monotonous with replacement of the white pulp by small to medium sized lymphoid cells with occasional plasmacytoid cells.

As a result of anti--CD20 therapy, CD20 immunostain (first image) is negative. However CD79a immunostain is strongly positive in all receptors at low power as well as that high-power confirming B-cell lineage.

The nodular B-cell clusters are positive for BCL-2 (bright) which additionally highlights background T cells.

Kappa and lambda in situ hybridization stains demonstrate that there is marked prominence of kappa light chain positive plasmacytic cells compared to lambda light chain stain indicating presence of kappa light chain restricted plasmacytic population allowing inference of clonality.

Additional flow cytometry showed that the CD19+ B cells comprise of only 1.55% of living cells with an exclusive Kappa light chain expression consistent with the ISH data.