Table 5:

Common IHC pitfalls that poses additional diagnostic challenge on cell-block IHC.

IHC	Common discrepancies
CD45	Lost expression in DLBCL (10%), T-LBL, and plasmacytoma/myeloma Aberrant expression in a subset of seminoma and mammary carcinoma
CD20	B-cells lack CD20 s/p immunotherapy “Rituximab” nucleolar staining of large number of cells of many different tissue types. Not indicating B-cell origin
CD3	Positive in NK-cells. ALCL is usually positive for CD3 but can be CD3 negative
CD10	Positive in Germinal center B and T-lymphocytes, Mature granulocytes, and subet of MZL
CD23	Positive in 20% of follicular lymphoma Normal in monocytes and dendritic cells
CD68	Positive in a subset of DLBCL Histiocytes
EMA	Positive in a subset of large B cell lymphoma, plasma cell myoma, Nodular lymphocyte predominant Hodgkin lymphoma, ALCL