Figure 1.

Immunohistochemical algorithm for separation of nodal marginal zone lymphoma (NMZL) from follicular lymphoma (FL). The algorithm starts at the top with a lymphoma that is considered to be either FL or NMZL. If all four germinal center markers (BCL6, CD10, LMO2, HGAL) are positive, a diagnosis of FL is made. If not, IRTA1 expression is determined. If IRTA1 is positive, a diagnosis of NMZL is made. If IRTA1 is negative, MNDA and germinal center markers are used to divide the remaining cases into three categories: NMZL for MNDA positive cases with positivity for none or only one germinal center marker, FL for MNDA negative cases with expression of 2 or 3 germinal center markers and low-grade B-cell lymphoma, unclassifiable for cases that do not fit into either of these two categories.