Nodal marginal zone lymphoma (NMZL) is an uncommon small B-cell lymphoma that is primary to lymph nodes but resembles the more common marginal zone lymphoma of mucosa-associated lymphoid tissue.
Sections show a lymph node, almost completely effaced by atypical lymphoid proliferation. Areas of sclerotic fibrosis are identified. The neoplastic cells are mainly small, monocytoid cells, with round to oval, irregular nuclear contours and small nucleoli. Some remnant germinal centres may be appreciable.

The immunostains show this to be a B-cell process (CD20, PAX5-positive). CD3 and CD5 highlight the minor, scattered T-cells. Cyclin D1 was negative (not shown). CD10 is negative in the majority of the atypical lymphocytes. Interestingly, a focal area with strong CD10 and Bcl-6 staining is observed, where the cells are also notable cleaved/twisted small B-cells.

Taken together, the diagnosis is a small B-cell lymphoma, negative for CD10 and CD5, consistent with marginal zone lymphoma. However, the area of intense germinal centre marker expression corresponds to follicular neoplasia in situ (see LMP90165 - In Situ Follicular lymphoma for another example, link in related content). In the absence of follicular neoplasm elsewhere, in situ follicular neoplasm carries <5% risk of subsequent follicular lymphoma. This lesion can be seen in conjunction with other B-cell lymphomas, as seen in this case.

This slide shows CD10 stain. See related content for H&E, CD3, CD5, CD20, CD21 and MIB1 stains.