Paediatric nodal marginal zone lymphoma (NMZL) has distinctive clinical and morphological characteristics.
It presents predominantly in males (with a male-to-female ratio of 20:1) with asymptomatic and localized disease (stage I in 90% of cases), mainly in the head and neck lymph nodes.
Histologically, it is similar to adult NMZL, except that there are often large follicles with extension of mantle zone B cells into the germinal centres, resembling progressively transformed germinal centres.
The immunophenotype is similar to that of adult NMZL, with expansion of the interfollicular areas by CD20+ B cells that commonly coexpress CD43.
IgD staining may help to delineate an irregular and expanded mantle zone.
BCL2 is positive in half of the cases. CD10 is usually negative.
Staining for CD279/PD1 shows numerous positive cells in the reactive germinal centres, a feature that may help in the differential diagnosis with paediatric-type follicular lymphoma, in which these cells are less numerous and pushed to the periphery of the germinal centre.
Clonal rearrangements of the IGHV region are detected in almost all cases. Trisomy 18 may be present in approximately one fifth of cases, and occasionally trisomy 3.
The prognosis of paediatric NMZL is excellent, with a very low relapse rate and long survival following conservative treatment.
The differential diagnosis with atypical marginal zone hyperplasia with monotypic immunoglobulin expression may be difficult, because the large cells in this condition also express CD43; although this type of hyperplasia has been reported in extranodal sites, some caution is advised because a similar process might also occur in the lymph nodes. Particularly for these reasons, genetic studies in paediatric marginal zone lymphomas are strongly recommended.
A marginal zone hyperplasia mimicking NMZL in head and neck lymph nodes of children has been associated with Haemophilus influenzae. The marginal zone cells in these cases are IgD-positive.