Paediatric marginal zone lymphoma and hyperplasia

Marginal zone lymphomas (MZL) are low-grade B-cell lymphomas arising from post-germinal memory B-cells occurring in adults with a slight female predilection. They are sub-categorized into nodal (NMZL), extra-nodal/mucosa-associated lymphoid tissue (MALT) and splenic (SMZL). MALT lymphomas are the most common (70%) followed by SMZL (20%) and NMZL (10%). Histologic transformation into aggressive B-cell lymphoma can rarely occur. MZL is extremely uncommon in the paediatric population and unlike in adults, is predominantly nodal. Paediatric NMZL (pNMZL) is an indolent, low-grade lymphoma with unique clinical and morphologic features. In contrast paediatric MALT lymphoma and SMZL are extremely uncommon and resemble their adult counterparts. Paediatric marginal zone lymphomas must be differentiated from paediatric-type follicular lymphoma (PFL) and marginal zone hyperplasia (MZH) of lymph nodes and mucosa-associated lymphoid tissue. This review summarizes the pathogenesis, morphology, genetic features of paediatric MZL and marginal zone hyperplasia. Recognition of these entities is important to avoid unnecessary therapy.